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## Thursday, 28 January 2021

### CBSE Class 12 Physics - MCQ and Online Tests - Unit 6 - Electromagnetic Induction

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 6 – Electromagnetic Induction

Every year CBSE conducts board exams for 12th standard. These exams are very competitive to all the students. So our website provides online tests for all the 12th subjects. These tests are also very effective and useful for those who preparing for competitive exams like NEET, JEE, CA etc. It can boost their preparation level and confidence level by attempting these chapter wise online tests.

These online tests are based on latest CBSE Class 12 syllabus. While attempting these our students can identify the weak lessons and continuously practice those lessons for attaining high marks. It also helps to revise the NCERT textbooks thoroughly.

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 6 – Electromagnetic Induction

Question 1.
In a uniform magnetic field B, a wire in the form of a semicircle of radius r rotated about the diameter of the circle with angular frequency ‘ω’. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R the mean power generated per period of rotation is :
(a) $$\frac{Bπr^2ω}{2R}$$
(b) $$\frac{(Bπr^2ω)^2}{8R}$$
(c) $$\frac{(Bπrω)^2}{2R}$$
(d) $$\frac{(Bπrω^2)^2}{8R}$$

Answer: (b) $$\frac{(Bπr^2ω)^2}{8R}$$

Question 2.
An e and a p are moving parallel to each other in a magnetic field. The magnetic force acting on the p+ is:
(a) 1840 times that on e
(b) less than that of e
(c) same as that of e
(d) slightly more than that of e

Answer: (c) same as that of e

Question 3.
A transformer is used to light 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A. Then the efficiency of the transformer is:
(a) 11%
(b) 50%
(c) 80%
(d) 90%

Question 4.
The magnetic flux (∅) lined with a coil is related to its area (s) as:
(a) ∅ ∝ s
(b) ∅ ∝ s²
(c) ∅ ∝ s1/2
(d) ∅ ∝ s-1/2

Question 5.
The coupling co-efficient of the perfectly coupled coils is:
(a) Zero
(b) 1
(c) slightly more than 1
(d) infinite

Question 6.
If the magnetic flux linked with a coil through which a current off ampere is set up is ∅, then the coefficient of self-inductance of the coil is:
(a) $$\frac{l}{∅}$$
(b) $$\frac{∅}{l}$$
(c) ∅l
(d) None of these

Answer: (b) $$\frac{∅}{l}$$

Question 7.
The magnetic field is parallel to a surface, then the magnetic flux through the surface is :
(a) zero
(b) small but not zero
(c) infinite
(d) large but not infinite

Answer: (b) small but not zero

Question 8.
The role of inductance is equivalent to:
(a) inertia
(b) force
(c) energy
(d) momentum

Question 9.
The flux linked with a coif at any instant t is given by ∅ = 10t² – 50t + 250. The induced emf at t = 35 is:
(a) 10 V
(b) 190 V
(c) -190 V
(d) -10 V

Question 10.
In the expression e = –$$\frac{d∅}{dt}$$, the -ve sign signifies:
(a) The induced emf is produced only when magnetic flux decreases
(b) The induced emf opposes the change in the magnetic flux
(c) The induced emf is opposite to the direction of the flux
(d) None of these

Answer: (b) The induced emf opposes the change in the magnetic flux

Question 11.
A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 rad s-1 . If the horizontal component of earth’s magnetism is 2 × 10-5 T, then e.m.f. developed between the two ends of the conductor is:
(a) 5 µV
(b) 50 µV
(c) 5 mV
(d) 50 mV

Question 12.
1 henry is equal to :
(a) $$\frac{weber}{ampere}$$
(b) $$\frac{weber}{Volt}$$
(c) weber ampere
(d) None of these

Answer: (a) $$\frac{weber}{ampere}$$

Question 13.
The magnetic flux (∅) linked with a coil is related to the number of turns (N) ofthe coil as:
(a) f ∝ N
(b) f ∝ N-1
(c) f ∝ N2
(d) f ∝ N-2

Question 14.
coil of L = 8.4 mH and R = 6 Ω is connected to a 12 V battery. The current in the coil is 1.0 A at approx’time of:
(a) 500 s
(b) 20 s
(c) 35 ms
(d) 1 ms

Question 15.
The core of a transformer is laminated because:
(a) rusting of core may be prevented
(b) ratio of voltage in primary and secondary may be increased.
(c) energy losses due to eddy current may be minimised
(d) The weight of transformer may be reduced

Answer: (c) energy losses due to eddy current may be minimised

Question 16.
If I current is flowing inductance L, then the dimension of $$\frac{3}{2}$$ LI² is equivalent to:
(a) charge
(b) force
(c) momentum
(d) energy

Question 17.
A choke is used as a resistance in :
(a) dc circuits
(b) ac circuits
(c) both ac and dc circuits
(d) neither (a) nor (b)

Question 18.
For purely capacitive circuits, power factor is:
(a) 0
(b) -1
(c) 1
(d) infinity

Question 19.
The magnetic flux linked with a coil is inversely proportional to the?
(a) magnetic field
(b) area of cross section
(c) number of turns
(d) none of these

Question 20.
Which of the following is not equal to a henry?
(a) $$\frac{Volt second}{ampere}$$
(b) $$\frac{Volt second^2}{Coulomb}$$
(c) $$\frac{Volt^2 second}{Coulomb}$$
(d) $$\frac{Jole second}{Coulomb^2}$$

Answer: (c) $$\frac{Volt^2 second}{Coulomb}$$

Question 21.
When the magnetic field is parallel to a surface, then the magnetic flux through the surface is:
(a) infinite
(b) zero
(c) small but not zero
(d) large but not infinite.

Question 22.
The phase difference between the flux linkage and the emf in a rotating coil in a uniform magnetic field is:
(a) zero
(b) $$\frac{π}{2}$$
(c) $$\frac{π}{4}$$
(d) π

Answer: (c) $$\frac{π}{4}$$

Question 23.
The energy stored in a 50 mH inductor carrying a current of 4 A is:
(a) 0.1 J
(b) 0.4 J
(c) 0.04 J
(d) 0.01 J

Question 24.
Two coils of self inductance 2 mil and 8 mil are placed so close together that the effective flux in one coil is completely linked with other. The mutual inductance between these coils is :
(a) 4 mH
(b) 16 mH
(c) 10 mH
(d) 6 mH

Question 25.
The SI unit of magnetic flux is:
(a) T
(b) Tn-2
(c) Wb
(d) Wb m-2