Current electricity

Class 12 · Physics · 6 questions

Name: ____________________ Date: ____________

The resistivity of a wire depends on:
- A Its area
- B Its material
- C Its current
- D Its length
A wire of resistance 4 ohm is stretched to double its length. Its new resistance is:
- A 2 ohm
- B 16 ohm
- C 4 ohm
- D 8 ohm
Kirchhoff's first law states that at a junction the sum of currents entering equals the sum:
- A Of resistances
- B Of voltages
- C Leaving
- D Of charges stored
A cell of emf 6 V and internal resistance 1 ohm drives a current through a 5 ohm resistor. What is the current?
- A 1.2 A
- B 6 A
- C 1 A
- D 0.5 A
The terminal voltage of a cell is less than its emf because of:
- A Temperature only
- B Its size
- C Internal resistance
- D Its colour
In a Wheatstone bridge, the bridge is balanced when the galvanometer shows:
- A Zero deflection
- B Maximum deflection
- C Infinite current
- D Negative deflection

Answer key

1. B, 2. B, 3. C, 4. C, 5. C, 6. A

Resistivity is a property of the material (and temperature), not of the wire's size.
Length doubles and area halves, so resistance is multiplied by 4.
This is conservation of charge.
I = emf / (R + r) = 6 / 6 = 1 A.
Part of the emf is lost across the internal resistance.
No current flows through the galvanometer when P/Q = R/S.