Vidaara.orgClass 12 · Physics
CodeVID-P12-03-EMI-01
Electromagnetic Induction — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all steps in numericals and draw neat labelled diagrams wherever asked. For full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The SI unit of magnetic flux is the:
- A.tesla
- B.weber
- C.henry
- D.volt
2.
Faraday's law relates induced EMF to:
- A.flux
- B.rate of change of flux
- C.current
- D.charge
3.
Lenz's law gives the:
- A.magnitude of EMF
- B.direction of induced current
- C.value of flux
- D.resistance
4.
Motional EMF is given by:
- A.$Bl/v$
- B.$Blv$
- C.$Bv/l$
- D.$lv/B$
5.
Eddy currents in transformer cores are reduced by:
- A.using thicker cores
- B.lamination
- C.increasing current
- D.removing the core
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define magnetic flux and give its SI unit.
7.
State Faraday's two laws of electromagnetic induction.
8.
A rod of length 0.4 m moves at 5 m/s perpendicular to a 0.5 T field. Find the motional EMF.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
State Lenz's law and explain how it conserves energy.
10.
What are eddy currents? Give one useful and one harmful effect.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Derive the expression for the motional EMF of a rod moving on rails in a magnetic field, and show it agrees with Faraday's law. Hence find the current and power dissipated if $B = 0.5\,\text{T}$, $l = 0.5\,\text{m}$, $v = 4\,\text{m/s}$, $R = 1\,\Omega$.
Answer Key
Section A — Multiple Choice Questions
- (B) weber
- (B) rate of change of flux
- (B) direction of induced current
- (B) $Blv$
- (B) lamination
Section B — Short Answer (2 marks)
- $\Phi = BA\cos\theta$; the number of field lines through a surface; unit weber (Wb).
- EMF is induced when flux changes; its magnitude equals the rate of change of flux, $\varepsilon = N\,d\Phi/dt$.
- $\varepsilon = Blv = 0.5 \times 0.4 \times 5 = 1\,\text{V}$.
Section C — Short Answer (3 marks)
- Induced current opposes the change in flux; the opposing force requires work, which becomes electrical energy.
- Induced loops in bulk conductors; useful in electromagnetic braking, harmful as heat loss in cores.
Section D — Long Answer (5 marks)
- $\varepsilon = Blv = 1\,\text{V}$; flux rate $= Blv$ confirms Faraday; $I = \varepsilon/R = 1\,\text{A}$; $P = I^2R = 1\,\text{W}$.
Generated by Vidaara.org · Assignment VID-P12-03-EMI-01 · vidaara.org