MOVING COIL GALVANOMETER

Galvanometer: 

A galvanometer is a device to detect current in a circuit. 

Principle: 

A current carrying coil placed in a magnetic field experiences a current dependent torque, which tends to rotate the coil and produces angular deflection. 

Construction:

A galvanometer consists f a rectangular coil of fine insulated copper wire wound on a light non magnetic metallic frame. The two ends of the axle of this frame are pivoted between two bearings. The motion of the coil is controlled by a pair of hair springs of phosphor bronze. The inner ends of the springs are soldered to the two ends of the coil and the outer ends are connected to the the binding screws. The springs provide the restoring torque and serve as current leads. A light aluminium pointer attached to the coil measures its deflection on a suitable scale. 

The coil is symmetrically placed between the cylindrical pole pieces of strong permanent horseshoe magnet. 

Theory and Working:

Let Ｉ = current flowing through the coil PQRS

     a, b = sides of the coil PQRS

       A  = ab = area of the coil

       θ = angle between the direction of B and normal to the plane of the coil.

       N = number of turns in the coil

Since the field is radial, the plane of the coil always remains parallel to the field B. Magnetic forces on the sides QR and SP are equal, opposite and collinear, so their resultant is zero. According to Fleming's left hand rule, the side PQ experiences a normal inward force equal to NＩbB why is the side QR experiences an equal normal out what force. The two forces on sides PQ and RS are equal and opposite. They form a couple and exert a torque given by 

τ = one of the force x perpendicular distance between them 

τ = F a sin θ = ＩbBa sin θ = ＩBA sin θ

[ ∵ ab = A]

If the rectangular loop has N turns, the torque increases N times ie.,

τ = NＩBA sin 90° = NＩBA

Here, θ = 90°, because the normal to the plane of coil remains perpendicular to the field B in all positions. 

The torque τ deflects the coil through an angle α. A restoring torque is set up in the coil due to elasticity of the springs such that

      τᵣ ∝ α   or   τᵣ = kα 

Where K is is the the torsion constant of the springs. 

Restoring Torque = Deflecting Torque

kα = NＩBA

Or  α = (NBA/k)Ｉ

Or      α ∝ Ｉ

Thus the deflection produced in the galvanometer coil is proportional to the current flowing through it. Consequently, the instrument can be provided with a scale with equal divisions along a circular scale to indicate equal steps in current. Such a scale is called linear scale.

Ｉ = (k/NBA) α = Ｉ = Gα

G = (k/NBA) is constant for a galvanometer and is called galvanometer constant for current reduction factor of the galvanometer.

TORQUE EXPERIENCED BY A CURRENT LOOP IN A UNIFORM MAGNETIC FIELD

Torque on a current loop in a uniform magnetic field:

A rectangular coil PQRS suspended in a uniform magnetic field B. The axis of the rectangular coil is perpendicular to the field. 

Let Ｉ = current flowing through the coil PQRS

     a, b = sides of the coil PQRS

       A  = ab = area of the coil

       θ = angle between the direction of B and normal to the plane of the coil.

 

Direction of the area and B makes an angle θ

all the forces acting on the sides of the rectangular coil PQRS

According to Fleming's left hand rule, 

i) the magnetic force on the side QR is F₁

 and it is acting upward.

F₁ = Ｉ(a xB) = ＩaB

ii) the magnetic force on the side SP is F'₁ and it is acting downward. 

F'₁ = Ｉ(a xB) = ＩaB

So, net force along vertical direction is zero as 

F₁ and F'₁ are equal and opposite as both are acting along the axis of the coil.

iii) the magnetic force on the side SR is F and it is coming out of the board.

F = Ｉ(b xB) = ＩbB

iv) the magnetic force on the side QP is F' and it is going into the board.

F' = Ｉ(b xB) = ＩbB

coil as seen from the top : m is the direction of the magnetic moment as well as coil area (perpendicular to the plane of the coil).

Therefore F and F' will produce a torque τ

We know, 

τ = one of the force x perpendicular distance between them 

τ = F a sin θ = ＩbBa sin θ = ＩBA sin θ

[ ∵ ab = A]

If the rectangular loop has N turns, the torque increases N times ie.,

τ = NＩBA sin θ

But there is one physical quantity called "magnetic moment" or m = NＩA

τ = m B sin θ = m x B

The direction of the torque τ is such that it rotates the loop clockwise about the axis of the loop. 

The torque will be zero when θ = 0 ie., When the plane of the loop is perpendicular to the magnetic field. 

The torque will be maximum when θ = π/2 and τ = NＩBA ie., when the plane of the loop is parallel to the magnetic field. 

Lecture- 5 : CLASS-X: SCIENCE : Chapter: REFLECTION OF LIGHT & NUMERICALS

CLASS X   |    SCIENCE    |    LIGHT

      notes prepared by subhankar Karmakar

                                                                         

Numericals on concave mirror:

Q1. What is the nature of a mirror having a focal length of, + 4 cm?

1. Ans. As the focal length is positive, the mirror is convex mirror. 

Q2. What kind of mirror can have a focal length of, - 6 cm?

2. Ans. As the focal length is negative, the mirror is a concave mirror. 

Q3. If the radius of curvature of a mirror is - 20 cm, what will be its focal length? What type of mirror it is? 

3. Ans. As the focal length is half of the the radius of curvature, so, f = -10 cm. As the  focal length is negative it is a concave mirror. 

Q4. Focal length of a small concave mirror is 2.5 cm. In order to use this concave mirror as a dentist's mirror, what must be the distance of tooth from the mirror?

4. Ans. As a dentist's mirror needs a real and magnified image of the tooth, the tooth must be placed in between pole and focus. Therefore, the distance of the tooth must be less than focal length of 2.5 cm. 

Q5. We wish to obtain an erect image of an object using a concave mirror of focal length 15 cm. 

a. What should be the range of distance of the object from the mirror?

b. What is the nature of the image?

c. Draw a ray diagram to show the image formation in this case. 

5. Ans. a. In order to obtain an erect image of an object with a concave mirror, the object should be at a distance less than its focal length. Therefore, here, the object must be placed at a distance less than 15 cm. 

        b. The nature of the image will be virtual. The image will be larger than the object

Q6. The image formed by a concave mirror is seen to be virtual, erect and larger than the object. Where should we place the object?

6. Ans. We should place the object in between pole and focus of the mirror. 

Q7. A concave mirror has a focal length of 20 cm. Where should an object be placed in front of this Concave mirror so as to obtain an image which is real, inverted and same size of the object?

7. Ans. When the object is placed at the centre of curvature, it produces an image, which is real, inverted and same size of the object. The distance of the centre of curvature from the pole is called radius of curvature and it is equal to twice of the focal length. 

Hence, the object must be placed at a distance (2x20 = 40 cm) 40 cm from the pole in front of the concave mirror. 

Q8. An object is placed in front of a concave mirror focal length 10 cm. Find the object distance if it produces a magnified real image?

8. Ans. If the object is placed in between focus and the centre of curvature,  then the image produce is real and inverted and magnified. Therefore, the object must be in between focus (f) and centre of curvature (2f). 

So, the object must be placed in between 10 cm to 20 cm from the pole in front of the mirror. 

Q9. An object is placed in front of a concave mirror focal length 5 cm. Find the object distance if it produces a diminished real image?

9. Ans. When the object is beyond the centre of curvature of the concave mirror it produces a diminished real image. Therefore the object must be at least more than 2f = 2x5 cm = 10 cm from the pole in front of the mirror.

Q10. An object is 20 mm in front of a concave mirror which produces an upright image or erect image. The radius of the curvature of the mirror is

a. Less than 20 mm       b. Exactly 40 mm

c. In between 20 mm and 40 mm

d. More than 40 mm. 

10. Ans. As for an erect image, object must be placed in between pole and focus, then focal length in this case is more than 20 mm. Therefore, the centre of curvature must be more than 2 x 20 mm = 40 mm. 

d. is the correct answer. 

Q11. Find the size, nature and position of image formed when an object of size 2 cm is placed at a distance of 9 cm from a concave mirror of focal length 6 cm. 

11. Ans. Focal length, f = - 6 cm and object distance, u = - 9 cm. Height of the object, h₁ = 2 cm. 

We know, mirror formula, 1/u + 1/v = 1/f

⟹ 1/v = 1/f - 1/u

⟹ 1/v = (u - f)/fu

⟹ v= fu/(u - f)

⟹ v = (-6)(-9)/( - 9 + 6) = (6x9)/(-3) 

∴ v = - 18 cm (position)

Magnification, 

m = (h₂/h₁) = (- v/u) = 18/(-9) = - 2

h₂ = m x h₁ = - 2 x 2 = - 4 cm (inverted)

Position: The image is 18 cm in front of the mirror. 

Nature: The image is real, inverted and magnified.

Size: The image is 4 cm high, inverted and twice magnified and below the principal axis.

Q12. An object 1 cm high is placed at a distance of 10 cm from a concave mirror which produces a real image 2 cm high. (i) what is the focal length of the mirror? (ii) find the position of the image.

Q13. A concave mirror produces three times magnified real image of an object placed at 8 cm in front of it. Where is the image located? What is the focal length of the mirror?

Q14. What is the nature of the image formed by a concave mirror if the magnification produced by the mirror is (i) +2 (ii) - 0.50 ?

Q15. An object is placed at a distance 8 cm from a concave mirror of focal length 12 cm. 

a. Draw a ray diagram for the formation of image.

b. Calculate the image distance.

c. State two characteristics of the image formed. 

Q16. At what distance from a concave mirror of focal length 12 cm should an object 1 cm long be placed in order to get an erect image 4 cm tall?

Q17. When an object is placed at a distance of 4 cm from a concave mirror, its image is formed at 6 cm behind the mirror. Calculate the focal length of the mirror. 

Q18. An object is placed in between principal focus and centre of curvature in front of a concave mirror. Draw a ray diagram to show how the image is formed, and describe its size, position and nature.

Lecture 1: CLASS XI : PHYSICS : CHAPTER - 5 : LAWS OF MOTION

FORCE: 

Force may be defined as an agency (a push or a pull) which changes or tends to change the state of rest or of uniform motion or the direction of motion of a body.

Effects produced by a force:

1. Force can change speed of an object.

When force is applied on a body the body starts to move. Again, when a force exerted by the brakes slows or stops moving train.

2. Force can change the direction of motion of an object.

Force exerted by a bat to a ball, changes the direction of the ball. 

3. Force can change the shape of an object. 

If we apply a force on a rubber ball, round shape of a rubber ball gets distorted.

Galileo's Laws of inertia:

A body moving with certain speed along a straight path will continue to move with same speed along the same straight path in the absence of external forces. 

INERTIA: 

The inherent property of a material body by virtue of which it cannot change, by itself, its state of rest or of uniform motion in a straight line is called inertia. 

Different types of inertia:

a. Inertia of rest: The tendency of a body to remain in its position of rest is called inertia of rest. 

Example: A person standing in a bus falls backward when the bus suddenly starts moving forward. 

b. Inertia of motion: The tendency of a body to remain in its state of uniform motion in a straight line is called inertia of motion. 

Example: When a moving bus suddenly stops, a person sitting in it falls forward. 

c. Inertia of direction: The inability of a body to change by itself its direction of motion is called inertia of direction.

Example: When a bus takes a sharp turn, a person sitting in the bus experiences a force acting away from the centre of the curved path. It is due to inertia of direction. 

Measurement of inertia of a body:

Mass of a body is the measure of its inertia. If a body has more mass, it has more inertia, it means it is more difficult to change its state of rest or of uniform motion. 

Linear momentum (p):

Momentum of a body is the quantity of motion possessed by the body. It is equal to the product of Mass and velocity of the body.

Momentum = mass x velocity 

Momentum is a vector quantity because the velocity v is a vector and mass m is a scalar. Its direction is same as the direction of the velocity of the body. Its magnitude is given by

p = mv

SI unit of momentum = kg m/s

CGS unit of momentum = g cm/s

The dimensional formula of momentum = [MLT⁻¹]

Q1. Two objects, each of mass m and velocities v₁ and v₂. If v₁> v₂, which one has more momentum?

Ans: p₁ = mv₁ and p₂ = mv₂

∴ (p₁/p₂) = (mv₁/mv₂) = (v₁/v₂)

As v₁> v₂ , so p₁> p₂

Q2. Two objects having mass m₁ and m₂ such that m₁> m₂ , and same velocity v. Which one has more momentum?

Ans: p₁ = m₁v and p₂ = m₂v

∴ (p₁/p₂) = (m₁v/m₂v) = (m₁/m₂)

As m₁> m₂ , so p₁> p₂

Q3. Two objects having same momenta (p₁ = p₂), if m₁> m₂, which one has more velocity?

Ans. p₁ = m₁v₁ and p₂ = m₂v₂

As p₁ = p₂

∴ m₁v₁ = m₂v₂ 

or  (v₂/v₁) = (m₁/m₂)

As m₁> m₂ , so v₁< v₂

Velocities of bodies having equal linear momenta are inversely proportional to their masses. 

So, when two objects have equal linear momentum, the lighter object will move faster than the heavier one. 

    

Lecture- 6 : CLASS-X: SCIENCE : Chapter: REFLECTION OF LIGHT & SIGN CONVENTIONS

CLASS X   |    SCIENCE    |    LIGHT

      Notes prepared by Subhankar Karmakar

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SCIENCE: CLASS X: CBSE (CLASS NOTES)

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SIGN CONVENTION FOR SPHERICAL MIRRORS:

According to the new cartesian sign convention:

1. All the distances are measured from pole of the mirror as origin. 

2. Distances measured in the same direction as that of incident light are taken as positive.

3. Distances measured against the direction of incident light are taken as negative.

4. Distances measured upward and perpendicular to the principal axis are taken as positive.

5. Distances measured downward and perpendicular to the principal axis are taken as negative. 

 

KEY POINTS TO REMEMBER

• The object is always placed on the left side of the mirror. 

• All the distances measured from the pole (P) of mirror to the right side will be considered positive and to the left side will be negative. 

• The object distance (u) is always negative.

• If an image is formed behind a concave mirror or to the right side of the mirror, the image distance (v) is positive, if the images formed in front of the mirror or to the left side of the mirror, then the image distance will be negative. 

• The image distance (v) for a convex mirror will be always positive.

• The focal length of a concave mirror is always negative

• The focal length of a convex mirror is always positive

• The height of an object is always positive

• If an image is formed above the principal axis its height is positive

• If an image is formed below the principal axis its height is negative

• The height of all the virtual and erect images is positive

• The height of all the real and inverted images is negative.

MIRROR FORMULA:

A formula which gives the relationship between image distance (v), object distance (u) and focal length (f) of a spherical mirror is known as the mirror formula. It is given as

1/v + 1/u = 1/f

Linear magnification produced by mirrors:

The ratio of the height of image to the height of object is known as linear magnification. It is also equal to the ratio of the image distance to the object distance, with a minus sign. 

∴  magnification = height of image/height of object

⟹ m = h₂ / h₁ = - v/u

h₁ = height of object

h₂ = height of image

• if the magnification has a plus sign, then the image is virtual and erect. 

• if the magnification has a negative sign, then the image is real and inverted. 

Position of the image means image distance.

Nature of image means whether  the image is "real and inverted" or "virtual and erect".

Size of image means value of magnification.

Lecture- 5 : CLASS-X: SCIENCE : Chapter: Reflection of light & concave mirror

CLASS X   |    SCIENCE    |    LIGHT

      Notes prepared by Subhankar Karmakar

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SCIENCE: CLASS X: CBSE (CLASS NOTES)

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 • Rules for obtaining images formed by Concave Mirror:

The image will be formed at the point where atleast two reflected rays intersect or appear to intersect. 

1. A ray of light which is is parallel to the principal axis of a concave mirror, passes through its focus after reflection from the mirror. 

2. A ray of light passing through the centre of curvature of a concave mirror is reflected back along the same path. Arrow pointing from left to right indicates the direction of incident ray and the arrow pointing from right to left indicates the direction of reflected ray.

3. A ray of light passing through the focus of a concave mirror becomes parallel to the principal axis after reflection.

4. A ray of light which is incident at the pole of a concave mirror is reflected back making the same angle with the principal axis. 

• If a ray of light is incident on a concave mirror along its principal axis, then it is reflected back along the same path. 

• FORMATION OF DIFFERENT TYPES OF IMAGES BY A CONCAVE MIRROR

The type of image formed by a concave mirror depends on the position of object in front of the mirror. At different places, an object produces different types of images. 

a. When the object is in between Pole (P) and focus (F):

When an object is placed between the pole (P) and focus (F) of a concave mirror, the image formed is:

i. Behind the mirror

ii. Virtual and erect, and

iii. Larger than the object or magnified.

Uses of concave mirror using this type of images:

1. A concave mirror can be used to magnify objects. Therefore, it will be used as a magnifying glass.

2. A concave mirror can be used as a makeup mirror. It magnifies a part of the face.

3. Dentist's mirror is a small concave mirror fitted in a frame with a long handle. It gives magnified image of tooth.

b. When the object is placed at the focus (F) of a concave mirror:

When an object is placed at the focus of a concave mirror, the image formed is:

i. At infinity, 

ii. Real and inverted, and

iii. Highly magnified.

Uses of concave mirror using this type of images:

1. When a light bulb is placed at the focus of a concave mirror reflector, the diverging light rays off the bulb are collected by the concave reflector and then reflected to produce a strong, parallel beam of light. 

c. When the object is placed between focus (F) and centre of curvature (C):

When an object is placed between the focus (F) and the centre of curvature (C) of a concave mirror, the image formed is:

i. Beyond the centre of curvature

ii. Real and inverted, and

iii. Larger than object or magnified.

d. When the object is placed at the centre of curvature (C) of a concave mirror:

When an object is placed at the centre of curvature (C) of a concave mirror, the image formed is:

i. At the centre of curvature (C),

ii. Real and inverted, and

iii. Same size as the object.

e. When the object is is beyond the centre of curvature (C) of the concave mirror:

When an object is placed beyond the centre of curvature (C) a concave mirror, the image formed is:

i. Between the focus (F) and the centre of curvature (C),

ii. Real and inverted, and

iii. Smaller than the object or diminished.

f. When the object is at infinity:

When an object is at infinity from a concave mirror, the image found is:

i. At the focus (F), 

ii. Real and inverted, and

iii. Much smaller than the object or highly diminished. 

"This means that a concave mirror can concentrate all The parallel rays of light to its focus."

Uses of concave mirror using this type of images:

1. A concave mirror is used as a "head mirror" by the doctors to concentrate light coming from a lamp onto the body part of a patient like ear, nose, throat etc. to be examined. 

2. The concave "metal dishes" are used in dish antenna of televisions to receive TV signals from the very distant communication satellite which are high up in the sky. 

USES OF CONCAVE MIRRORS:

1. A concave mirror can be used to magnify objects. Therefore, it will be used as a magnifying glass.

2. A concave mirror can be used as a makeup mirror. It magnifies a part of the face.

3. Dentist's mirror is a small concave mirror fitted in a frame with a long handle. It gives magnified image of tooth.

4. When a light bulb is placed at the focus of a concave mirror reflector, the diverging light rays off the bulb are collected by the concave reflector and then reflected to produce a strong, parallel beam of light. 

5. A concave mirror is used as a "head mirror" by the doctors to concentrate light coming from a lamp onto the body part of a patient like ear, nose, throat etc. to be examined. 

6. The concave "metal dishes" are used in dish antenna of televisions to receive TV signals from the very distant communication satellite which are high up in the sky. 

LECTURE -2 : CLASS VIII : SCIENCE : CHAPTER 4 : MATERIALS : METALS & NON-METALS

CLASS VIII   |    SCIENCE    |    CHAPTER 4

     Notes prepared by Subhankar Karmakar 

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CHEMICAL PROPERTIES OF METALS & NON METALS:

REACTION OF METALS:

 a. Reactions of metal with Oxygen (O₂):

 Metal reacts with oxygen to form metal oxides. Metal oxides are basic in nature. 

The basic metal oxides turn red litmus to blue. 

*(Metals and R & B)

∴ Metal + Oxygen (from air) = Metal Oxide (basic oxide) 

Magnesium burning in air: 

I. When Magnesium (Mg) burns in air, it combines with the oxygen (O₂) of air to form magnesium oxide. 

• Mg + O₂ = MgO (a basic oxide)

II. Magnesium oxide dissolves partially in water to form magnesium hydroxide Mg(OH)₂  solution:

• MgO + H₂O = Mg(OH)₂ (a base)

Sodium (Na) reacts with Oxygen in air and produces Sodium Oxide (Na₂O)

• Na + O₂ = Na₂O (a basic oxide) 

Water solution of Sodium Oxide forms Sodium Hydroxide (NaOH)

• Na₂O +  H₂O  = NaOH

 Reaction of iron with oxygen of air:

During the rusting of iron, iron (Fe) metal combines slowly with the oxygen (O₂) of air in the presence of water or moisture to form a compound called iron oxide (Fe₂O₃). This iron oxide is called rust. Damp air contains Oxygen (O₂) + water (H₂O). 

• Iron (Fe) + Oxygen (O₂) + water (H₂O) ⟹ Iron Oxide or rust (Fe₂O₃) (basic oxide)

• Reaction of copper metal with moist air:

When a copper object is exposed to moist air for a long time, then copper (Cu) reacts with water (H₂O), carbon dioxide (CO₂) and oxygen (O₂) present in moist air to form a green coating on the copper object. The green coating is a mixture of copper hydroxide [Cu(OH)₂] and copper carbonate (CuCO₃) which is formed by the action of moist air on copper object.

• 2Cu + H₂O + CO₂ + O₂ = Cu(OH)₂ + CuCO₃ 

• Corrosion of copper: The formation of green coating of basic copper carbonate on the surface of copper objects on exposure to moist air is called corrosion of copper. 

 

b. Reactions of metal with water:

 When a metal reacts with water, then a metal hydroxide and hydrogen gas are formed. 

Metal + water = Metal hydroxide + Hydrogen

Not all metals react with water. Some of the metals reacts with cold water, whereas some metals reacts with hot water and steam. It depends upon reactivity of metals.

Sodium and potassium very quickly reacts with cold water. 

·        Magnesium reacts slowly with cold water and quickly with hot water and zinc and iron slowly react with steam. 

·        Sodium (Na) + water (H₂O) → Sodium Hydroxide (NaOH) + Hydrogen (H₂)

·       Sodium (Na) is a very reactive metal. It reacts with moisture, oxygen and other gases present in air. So, if sodium metal is kept exposed to air, it will react with the various components of air and get spoiled. In order to prevent its reaction with the moisture and other gases of air, sodium metal is always told under kerosene. Potassium metal is also very reactive and also kept in kerosene. 

c. Reactions of metals with acids:

Most of the metals react with dilute acids to form salts and hydrogen gas. 

Metal + Acid → Salt + Hydrogen gas.

Only less reactive metals like Copper, silver and gold do not react with dilute acids. 

• Magnesium reacts with dilute hydrochloric acid to form magnesium chloride (salt) and hydrogen gas.

Magnesium + hydrochloric acid → magnesium chloride + hydrogen gas

Mg + HCl → MgCl₂ + H₂

 When foodstuffs containing acids like orange juice, pickles, and curds are kept in iron, aluminium or copper containers, the acids present in them react with the metal of the container slowly to form toxic salts. That's why acidic foodstuffs should not be kept in metal containers.

d. Reactions of metal with bases:

Only some metals react with bases to form salts and hydrogen gas. Like aluminium is a metal and Sodium hydroxide is a base. When aluminium is heated with sodium hydroxide solution, then sodium aluminate which is a salt and hydrogen gas is formed. 

Sodium hydroxide + aluminium → sodium aluminate + hydrogen

NaOH + Al → NaAlO₂ + H₂

Zinc also reacts with bases like sodium hydroxide to produce hydrogen gas. 

REACTION OF NON METALS:

a. Reaction of nonmetals with oxygen:

 Non metals react with oxygen to form non metal oxides. Non metal oxides are acidic in nature. Non metal oxides water solution turn blue litmus into red. 

Non metal + oxygen → non metal oxide

 1. When sulphur burns in air, it combines with the oxygen of air to form sulphur dioxide. Sulphur dioxide is a acidic oxide. 

Sulphur + oxygen → sulphur dioxide

S + O₂ → SO₂

Sulphur dioxide dissolves in water to form sulphurous acid solution

SO₂ + H₂O → H₂SO₃

b. Reactions of nonmetals with water:

 Non metals do not react with water. Therefore, highly reactive nonmetals like phosphorus cannot be kept open in the air as it reacts with oxygen of air and catches fire. So, in order to protect phosphorus from atmospheric air, it is stored in a bottle containing water.

 c. Reactions of nonmetals with acids:

 Non metals do not react with dilute acids. 

 d. Reactions of nonmetals with bases:

 Some of the nonmetals react with bases but no hydrogen gas is produced.

 Difference between metal oxides and non metal oxides:

 Metal oxides are basic in nature and turn red litmus to blue. 

Non metal oxides are acidic in nature and turn blue litmus to red. 

 REACTIVITY SERIES OF METALS:

The arrangement of metals in a vertical column in the order of decreasing reactivities is called the reactivity series of metals.  

In reactivity series, the most reactive metal is placed at the top whereas the least reactive metal is placed at the bottom.

Potassium is the most reactive metal, so it has been placed at the top of the reactivity series. Gold is the least reactive metal so it has been placed at the bottom of the reactivity series.

 

Potassium (K) (most reactive)

Sodium (Na)

Calcium (Ca)

Magnesium (Mg)

Aluminium (Al)

Zinc (Zn)

Iron (Fe)

Lead (Pb)

Copper (Cu)

Silver (Ag)

Gold (Au) (least reactive)

Reactivity of the metals decreases as we go down in the above series. 

 

LECTURE -1 : CLASS VIII : SCIENCE : CHAPTER 4 : MATERIALS : METALS & NON-METALS

CLASS VIII   |    SCIENCE    |    CHAPTER 4

      notes prepared by subhankar Karmakar

                                                                         

• Element:

A substance which cannot be broken down into two or more simpler substances by chemical reactions is is called an element. 

Some of the common elements are:

Hydrogen, helium, carbon, nitrogen, oxygen, sulphur, phosphorus, silicon, chlorine, bromine, iodine, sodium, potassium, magnesium, calcium, zinc, iron, copper, silver, gold and mercury. 

Every element is represented by a symbol. No two elements can have the same symbol.

Symbols of common elements:

1. Hydrogen - H

2. Helium - He

3. Carbon - C

4. Nitrogen - N

5. Oxygen - O

6. Sulphur - S

7. Phosphorus- P

8. Silicon - Si

9. Chlorine - Cl

10. Bromine - Br

11. Iodine - I

12. Sodium - Na

13. Potassium - K

14. Magnesium - Mg

15. Calcium - Ca

16. Zinc - Zn

17. Iron - Fe

18. Copper - Cu

19. Silver - Ag

20. Gold - Au

21. Mercury - Hg

• Atom:

The smallest particle of an element is called atom. An element is a substance which is made up of only one kind of atoms. 

There are as many type of atoms as are elements. So different elements are made up of different kinds of atoms. For example, sulphur element is made up of only sulphur atoms. This means an amount of oxygen is totally made of atoms of oxygen only. 

There are only 92 naturally occurring elements known to us at present. Other elements in the periodic table are synthesized elements. 

Properties of elements:

Different elements have different properties. Some of the most important properties of elements are malleability, ductility, brittleness, lustre, Sonorousness, conductivity, strength, hardness, toughness etc. 

On the basis of their properties, all the elements can be divided into two main groups: 

Metals and nonmetals.

Characteristics of metals:

Metals are malleable and ductile elements. They are good conductors of heat and electricity. Metal are lustrous or shiny. Metals are usually hard and strong. All the metals are solids except Mercury which is a liquid metal. Metals have high densities which means they are heavy. Metals have high melting points and boiling points. Metals are sonorous which means that metals make a ringing sound when we strike them with a hard object. 

Some of the examples of metals are: iron, copper, aluminium, zinc, silver, gold, Platinum, chromium, sodium, potassium, calcium, magnesium, nickel, Cobalt, tin, Mercury, tungsten, manganese, uranium etc. Out of 92 naturally occurring elements, 70 elements are metal.

Characteristics of nonmetals:

Non metals are the elements which are neither malleable nor ductile, they are brittle. Non metals do not conduct heat and electricity. Non metals are not lustrous or shiny. Non metals can be solid, liquid or gases at the room temperature. Non metals have usually low melting points and boiling points. Non metals have low densities which means they are light. Non metals are not sonorous, which means non metals do not make ringing sound when we strike them with a hard object. 

Some of the examples of non metals are: Carbon, sulphur, phosphorus, hydrogen, oxygen, nitrogen, chlorine, fluorine, bromine, iodine, helium, neon, argon, Krypton and xenon. Out of of 92 naturally occurring elements, 22 elements are non metals. Out of these, 10 non metals are solids, 1 non metal is a liquid (bromine), and 11 non metals are gases. 

Metalloids:

There are some elements which show some properties of metals and the other properties of nonmetals. The elements whose properties are intermediate between those of metals and nonmetals are known as metalloids. 

The example of metalloids are: silicon, germanium, arsenic and tellurium.

Physical properties of metals and nonmetals:

a. Malleability:

The property which allows the metals to be hammered into thin sheets is called malleability. Most of the metals are malleable. Gold and silver are the best malleable metals and can be hammered into very fine sheets or foils. Aluminium and copper are also highly malleable. It is due to the property of malleability that metals can be bent to form objects of different shapes by beating with a hammer. 

Non metals are not malleable.

b. Brittleness:

The property due to which non-metals  break on hammering is called brittleness. This means non metals can not be hammered into a thin sheets, it break into small pieces when hammered. All the non metals are brittle.

c. Ductility:

The property which allows the metals to be drawn into wires is called ductility. Ductility is another characteristics property of metals. Generally all the metals are malleable and ductile. 

Gold and silver are among the best ductile metals. Copper and aluminium metals are also very ductile and can be drawn into to tin Copper and aluminium wires.

Non metals are not ductile. 

d. Conductivity:

Heat and electricity can easily flow through metals. Therefore metals are good conductors of heat and electricity. ( as they allow heat and electricity to pass through them easily).

Silver metal is a best conductor of heat. Copper, gold, aluminium and iron metals are good conductors of heat.

Except graphite and diamond all the non metals are bad conductors of heat and electricity. Therefore, they are called insulators. Diamond is a good conductor of heat whereas graphite is a good conductor of electricity. 

e. Lustre:

All the metals have a shiny appearance. This property of metal is known as Lustre of metal. 

All the non metals are not lustrous. Only iodine has a lustre. 

f. Strength:

Metals are usually strong, they have high tensile strength. Metals can hold large weights without snapping. Iron is one of the most strongest material, hence iron is used in construction purposes. 

Non metals are not strong. They have low tensile strength.

g. Sonorousness:

All the metals make a ringing sound when we strike them. This property of metal is known as Sonorousness. Sonorous means capable of producing a ringing sound. 

Non metals are not sonorous. They do not produce ringing sounds when we strike them. 

h. Hardness:

Metals cannot be cut very easily. This property is known as hardness of metal. Only sodium and potassium metals are soft and can be easily cut with a knife. 

Most of the solid non metals are quite soft.

Differences in physical properties of metals and nonmetals

1. Metals: metals are malleable and ductile. 

    Non metals: non metals are neither malleable nor ductile. They are brittle.

2. Metals: metals are good conductors of heat and electricity.

Non metals: nonmetals are poor conductors of heat and electricity except graphite is a good conductor of electricity and diamond is a good conductor of heat.

3. Metals: metals are lustrous. 

Non metals: non metals are not lustrous. They are dull. Only iodine has shiny appearance.

4. Metals: Metals are strong and have a high tension strength. Only sodium and potassium are not strong and have low tensile strength.

Non metals: non metals are not strong. They have a low tensile strength.

5. Metals: metals of sonorous. They make a ringing sound when struck.

Non metals: non metals are not Sonorous. They do not make a ringing sound when struck.

6. Metals: Metals are generally hard. Only sodium and potassium are soft metals.

Non metals: solid nonmetals are quite soft. Only diamond are very hard, in fact it is the hardest material. 

Lecture-1, 2, 3 and 4 : CLASS-X: SCIENCE : Chapter: Reflection of light & concave mirror

CLASS X   |    SCIENCE    |    LIGHT

      Notes prepared by Subhankar Karmakar

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click to access other class notes

SCIENCE: CLASS X: CBSE (CLASS NOTES)

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CLASS- X; PHYSICS; CHAPTER-1

Topic: REFLECTION OF LIGHT

LECTURE-1

Characteristics of Light:

1. Light is a form of energy.

2. Light always travelled in a straight line which is called Rectilinear Propagation of Light.

3. Light can travel through a medium as well as through vacuum also.

4. Light carries Energy from one point to another point.

5. Physics of light is called Optics.

6. Light exhibits two phenomena called Reflection and Refraction of Light.

REFLECTION OF LIGHT

• When a ray of light travelling in one medium falls on the surface of the second medium and turned back into the first medium, then it is called reflection of light. 

Important characteristics of reflection of light:

• The objects having polished, shining surfaces reflect more light than objects having unpolished, dull surfaces.

• Silver metal is one of the best reflectors of light.

• Ordinary mirrors are made by depositing a thin layer of silver metal on the back side of a plane glass sheet. The Silver layer is then protected by a coat of red paint. The reflection of light in a plane mirror takes place at the Silver surface in it. 

• A ray of light it is the straight line along which light travels.

• A bundle of light rays is called a beam of light.

INCIDENT RAY: The ray of light travelling in one medium when falls on the surface of the second medium is called incident ray.

REFLECTED RAY: The ray of light which after striking the surface of the second medium and turned back into the first medium is called reflected Ray.

POINT OF INCIDENCE: The point where incident ray strikes the surface of the second medium is called point of Incidence.

NORMAL: Perpendicular to the surface of the second medium drawn at the point of Incidence is called Normal.

ANGLE OF INCIDENCE: The angle between incident ray and normal is called angle of incidence. It is denoted by ∠i.

ANGLE OF REFLECTION: The angle between reflected ray and normal is called angle of reflection. It is denoted by ∠r.

LAWS OF REFLECTION:

Reflection of light takes place according to the following two laws:

First law of reflection:

1. The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.

Second law of reflection:

2. The angle of incidence is always equal to the angle of reflection, i.e., ∠i = ∠r.

• A ray of light which is incident normally or perpendicularly on a mirror, is reflected back along the same path ( because the angle of incidence as equal as the angle of reflection for such a Ray of light are zero).

• The laws of reflection of light applied to all kinds of mirrors, plane mirrors as well as spherical mirrors.

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LECTURE-2

Regular reflection:

• In regular reflection, a parallel beam of incident light is reflected as a parallel beam in one direction. Regular reflection of light occurs from smooth surfaces like that of a plane mirror or highly polished metal surfaces. A plane mirror always produces regular reflection of light.

Diffuse reflection of light:

• In diffuse reflection, a parallel beam of incident light is reflected in different directions. The diffuse reflection of light takes place from rough surfaces like paper, cardboard, chalk, table, chair and unpolished metal surfaces.

 

Objects: Anything which gives out light rays either its  own or reflected by it, is called an object. For example, a bulb, a candle, a pinhead, an arrow etc. 

Images: Image is an optical appearance produced when light rays coming from an object are reflected from a mirror for refracted through a lens. For example, when we look into a mirror, we see the image of our face, while watching a movie in the cinema hall, we see the images of actors and actresses on the cinema screen. 

Types of images:

There are two types of images

a. Real image 

b. Virtual image

Real image: The image which can be obtained on a screen is called a real image. The image formed on a cinema screen is an example of real image. 

Virtual image: The image which cannot be obtained on a screen is called a virtual image. A virtual image can be seen only by looking into a mirror or a lens. The image of our face in a plane mirror is an example of virtual image. A virtual image is just an illusion. 

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LECTURE-3

Formation of image in a plane mirror: 

Consider a small object O placed in front of a plane mirror MM'. The mirror will form an image I of the object O. The object O gives out light rays OA and OB. OA coming from the object O is incident on the plane mirror at point A and it gets reflected in the direction AX according to the laws of reflection of light, making the angle of reflection r₁ equal to the angle of incidence i₁. Another ray of light OB coming from the object O strikes the mirror at point B and gets reflected in the direction BY, again making the angle of reflection r₂ equal to the angle of incidence i₂. 

The two reflected rays AX and BY are diverging from each other so they cannot meet under left side of the mirror. Let us produce the reflected rays AX and BY backwards. They meet at point I behind the mirror. Now, when the reflected rays AX and BY enter the eye of a person at position E, the eye sees the rays of light in the straight line direction in which the reflected rays enter it. So, the person looking into the mirror from position E sees the reflected rays as if they are coming from the point I behind the mirror. Thus, point I is the image of the object O formed by the plane mirror.

• The nature of image formed by a plane mirror is virtual and erect. The size of the image formed by a plane mirror is equal to that of the object. 

• The image formed in a plane mirror is at the same distance behind the mirror as the object is in front of the mirror.

Lateral inversion: 

• When an object is placed in front of a plane mirror, then the right side of object appears to become the left side of image, and the left side of object appears to become the right side of image. This change of sides of an object and its mirror image is called lateral inversion. 

• The phenomenon lateral inversion is due to the reflection of light. 

Characteristics of an image formed by a plane mirror:

a. The image formed in a plane mirror is virtual. It cannot be received on a screen.

b. The image formed in a plane mirror is erect. It is the same side up as the object.

c. The image in a plane mirror is of the same size as the object.

d. The image formed by a plane mirror is at the same distance behind the mirror as the object is in front of the mirror. 

e. the image formed in a plane mirror is laterally inverted.

Uses of plane mirrors:

a. Plane mirrors are used to see ourselves. The mirrors on our dressing table and in bathroom are plane mirrors.

b. Plane mirrors are fixed on the inside walls of certain shop to make them look bigger.

c. Plane mirrors are fitted at blind turns of some busy roads so that drivers can see the vehicle coming from the other side and prevent accidents.

d. Plane mirrors are used in making periscopes. 

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LECTURE-4

SPHERICAL MIRRORS:

A spherical mirror is a reflecting surface which forms part of a hollow sphere. 

(a) A hollow sphere cut by a plane                          (b) concave mirror  (c) convex mirror

Spherical mirrors are of two types: 

(i) Concave Mirror: A spherical mirror in which the outer bulged surface is silvered polished and the reflection of light takes place from the inner hollow surface is called a concave mirror.

(ii) Convex Mirror: A spherical mirror in which the inner hollow surface is silvered polished and the reflection of light takes place from the outer bulged surface is called convex mirror.

Terms related with Spherical Mirrors

1. POLE: It is the middle point P of the spherical mirror.

2. CENTRE OF CURVATURE: It is the centre C of the sphere of which the mirror forms a part.

3. RADIUS OF CURVATURE: It is the radius ( R= AC or BC) of the sphere of which the mirror forms a part.

4. PRINCIPAL AXIS: The line PC passing through the pole and the centre of curvature of the mirror is called its principal axis.

5. APERTURE: It is the diameter AB of the circular boundary of the spherical mirror.

6. PRINCIPAL FOCUS: A narrow beam of light parallel to the principal axis either actually converges to or appears to diverge from a point F on the principal axis after reflection from the spherical mirror. This point is called the principal focus of the mirror.

CONCAVE MIRROR:

7. Principal focus of a concave mirror:

The principal focus of a concave mirror is a point on its principal axis to which all other light rays which are parallel and close to the axis,  converge after reflection from the concave mirror

8. Focus of a concave mirror:

A concave mirror has a real focus. The focus of a concave mirror is in front of the mirror. 

9. Focal length of a concave mirror: 

The focal length of a concave mirror is the distance between its pole and principal focus. It is denoted by f. 

10. Relation between radius of curvature (R) and focal length (f) of a spherical mirror:

The focal length of a spherical mirror is equal to half of its radius of curvature. It is true for both concave and convex mirror. 

∴ f = R/2

Principal focus and focal length of a convex mirror: 

• The principal focus of a convex mirror is a point on its principal axis from which a beam of light rays, initially parallel to the axis, appears to diverge after being reflected from the convex mirror. 

• A convex mirror has virtual focus, focus of a convex mirror is situated behind the mirror.