Question

In the activity conducted above, touch the free end J at E and slowly slide it from E to P

(i) What change occurred in the intensity of light from the bulb?

(ii) What may be the reason behind the change?

(iii) What is the working principle of a rheostat?

(iv) What is the symbol of a rheostat?

(v) Analysis the completed table and write down the inferences.

Answer 1

(i) Intensity of light increases gradually.

(ii) As the length of the conductor decreases, resistance and current increases.

(iii) If the potential difference is constant, then the current is inversely proportional to the resistance. For a conductor of uniform area of cross-section, the length of a conductor and the resistance are directly proportional.

Rheostat is a device used to regulate the current in a circuit by changing the resistance

(iv) 

(v) The resistance of a conductor increases with the increases in the length of the conductor.

R α l

The resistance of a conductor decreases with increases in the area of cross-section.

R α I/A that is R α I/A

R = a constant × l/A

R = \(p\frac{1}{A}\)

P = RA/l

P is the resistivity of the material the conductor is made of. The length of a conductor of resistance R Q is 1m and its area of cross-section is 1m². Calculate the resistivity of the material the conductor is made of. length, l = 1m

Area of cross-section, A = 1m²

Resistivity \(P=\frac{RA}{1}=\frac{R\times1}{1}\) P = R

Resistivity of a substance is the resistance of the conductor of unit length and unit area of cross-section. The resistivity of a substance is a constant at fixed temperature. But it will be different for different materials.

Unit of resistivity =

The Unit of resistivity is Qm 

Let’s get acquainted with some of the tools related to electric current: 

We use many electric devices in our everyday life. Different tools are needed to connect these devices with the electric line and to perform maintenance. They are enlisted here.