## OHMS’ LAW

The potential difference, V, across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same.

## Formula: Where, R is a constant for the given metallic wire at a given temperature and is called its resistance.

## Graph: The V–I graph is a straight line that passes through the origin of the graph, as shown in Figure. Thus,
is a constant ratio.

## Other topic on this chapter: 1.   Electric Current. 2.   Electric Potential 3.   Ohm's Law 4.   Resistance and resistivity 5.   Combinations of resistors 6.   Heating effect of electric current 7.   Electric power

1. Name and state the law which relates the current in a conductor to the potential difference across a conductor and the current flowing through it.

2. Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

3. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

4. (a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω? (b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω?

5. The potential difference between the terminals of an electric heater is 60 V when it draws a current of
4A from the source. What current will the heater draw if the potential difference is increased to 120 V?

6. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below –
I (amperes) 0.5    1.0     2.0      3.0       4.0
V (volts)     1.6    3.4     6.7     10.2     13.2
Plot a graph between V and I and calculate the resistance of that resistor.

7. Keeping the potential difference constant, the resistance of a circuit is doubled. By how much does the current change?