Lecture-3 : CLASS-X: SCIENCE : Chapter: Electricity

CLASS X: SCIENCE: ELECTRICITY

notes prepared by Subhankar Karmakar

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ELECTRIC CHARGE: (Q)

Electric charge is the property that causes electrically charged particles to attract or repel each other.

There are two types of electric charge, positive and negative. Protons are positively charged particles, while electrons are negatively charged particles. Neutrons have no electric charge.

Opposite charges attract each other, while like charges repel each other. The strength of the electric force between two charged particles depends on the magnitude of the charges and the distance between them. The greater the charge and the closer the distance, the stronger the electric force between them.

Electric charge is measured in coulombs (C). The unit of electric charge is the amount of charge that flows through a wire when a current of one ampere flows for one second.

Electric charge plays a fundamental role in many areas of science and technology, including electricity, electronics, magnetism, and chemistry.

ELECTRIC CURRENT: (I)

Electric charge flows through a wire if potential difference is applied between the end of the wire. 

When electric charge flows through a wire , it is called electric current. Therefore, the electric current is a flow of electric charges in a conductor such as a metal wire. 

The magnitude of electric current in a conductor is the amount of electric charge passing through a given point of the conductor in one second. 

If a charge of Q coulombs flows through a conductor in time t seconds, then the magnitude I of the electric current flowing through it is given by:

FORMULA OF ELECTRIC CURRENT:

Current, I = Q/t

UNIT OF ELECTRIC CURRENT:

The SI unit of electric current is ampere. It is denoted by the symbol A. 

DEFINITION OF 1 AMPERE CURRENT:

1 A current : When 1 coulomb of charge flows through any cross section of a conductor  in 1 second, the electric current flowing through it is said to be 1 ampere. 

1 ampere = 1 coulomb / 1 second

Or, 1 A = 1 C/1 s

There are two smaller unit of current called

1. milliampere (mA) and 2. microampere (μA)

1 milliampere (1 mA)= 1/1000 A = 10⁻³ A 

1 microampere (1 μA) = 1/1000000 A = 10⁻⁶ A

AMMETER:

Electric current is measured by an instrument called ammeter. An ammeter is always connected in series with the circuit in which the current is to be measured. Since the entire current passes through the ammeter, therefore, an ammeter should have very low resistance, so that it may not change the value of the current flowing in the circuit. 

CONTINUOUS FLOW OF ELECTRIC CURRENT:

If we maintain a steady potential difference between the two ends of a conductor so as to get a continuous flow of current is to connect the conductor between the terminals of a cell or a battery.

DIRECTION OF ELECTRIC CURRENT:

The conventional direction of electric current is from positive terminal of a cell or a battery to the negative terminal through the outer circuit. The actual flow of electrons which is really responsible for the electric current is however from negative terminal to positive terminal of a cell which is opposite to the direction of conventional current.

Electric current flows through a conductor due to the presence of free electron in the conductor. The electron which can move easily through a conductor is known as a free electron. 

ELECTRIC CIRCUITS:

A continuous conducting path consisting of wires and other resistances like electric bulb and a switch, between the two terminals of a cell or a battery along which an electric current flows is called an electric circuit.

Symbols for Electrical Components:

a. Cell : It supplies a continuous supply of potential difference.

b. Battery or Combination of cells:

c. Connecting Wire: It is made of conductors with a covering of insulator through which electric current can flow

d. A Wire Joint: A joint where two connecting wire is joined together. 

e. Wires crossing without connection:

When two wires cross each other without touching each other

f. Fixed Resistance or Resistor:

When the value of the resistor does not change.

g. Variable Resistance or Rheostat:

When the value of the resistor can change with time.

h. Ammeter: instrument which measures current.

i. Voltmeter: instrument which measures potential difference.

j. Galvanometer: instrument which detects the flow of current through a wire.

k. An open switch: which prevents the flow of current through a circuit.

l. A closed switch: which enables electric current to flow through a circuit.

m. Electric bulb: which emits light when electric current flow through it.

Circuit Diagrams:

A diagram which indicates how different components in a circuit have been connected by using the electrical symbols for the components, is called a circuit diagram. 

A simple electric circuit. In this circuit, a resistor R has been connected to the two terminals of a cell through a switch (which is closed). An ammeter A has been put in series with the resistor R. This is to measure current in the circuit. A voltmeter V has been connected across the ends of the resistor R, that is, voltmeter is connected in parallel with the resistor. This voltmeter is used to measure potential difference or voltage across the ends of the resistor R.