Current electricity

Written by Dr. Hamza Farooq (Physics)

Class 12 · Physics · 9 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
The unit of resistivity is the:
- A Ohm
- B Ohm per metre
- C Siemens
- D Ohm metre
Internal resistance of a cell makes its terminal voltage ___ the emf when current flows.
- A Double
- B Greater than
- C Less than
- D Equal to
Joule's law of heating says that the heat produced is proportional to:
- A I R
- B R / t
- C I² R t
- D V / R

Answer key

1. B, 2. B, 3. C, 4. C, 5. C, 6. A, 7. D, 8. C, 9. C

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.
rho = R A / L, so ohm metre.
Some voltage is lost inside the cell.
H = I² R t.