Chapter 11 Solutions — Electricity

An electric circuit is a continuous and closed path through which electric current flows.

A circuit consists of:

- A source of electrical energy (cell or battery)

- Connecting wires (conductors)

- A switch (to open or close the circuit)

- An electrical device (load) such as a bulb, resistor, etc.

When the circuit is closed (switch ON), current flows from the positive terminal of the battery through the external circuit to the negative terminal.

When the circuit is open (switch OFF), the path is broken and no current flows.

A battery (or a cell) helps to maintain a potential difference across a conductor.

The chemical energy stored in the battery gets converted into electrical energy. The battery does work to drive the positive charges from its negative terminal to its positive terminal inside the battery, thereby maintaining a constant potential difference across the conductor connected to it.

As long as the battery is connected and has energy, it continuously maintains the potential difference, ensuring a steady flow of current.

The resistance of a conductor depends on the following factors:

1. Length (l): Resistance is directly proportional to the length of the conductor.

R is proportional to l

(Doubling the length doubles the resistance)

2. Cross-sectional area (A): Resistance is inversely proportional to the area of cross-section.

R is proportional to 1/A

(Doubling the area halves the resistance)

3. Nature of the material: Different materials have different resistivities (rho).

Metals like copper and silver have low resistivity, while nichrome and tungsten have high resistivity.

4. Temperature: Resistance of metals increases with increase in temperature. For semiconductors, resistance decreases with increase in temperature.

Combining factors 1, 2, and 3:

R = rho x l / A

where rho (resistivity) depends on the material.