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#### Electromagnetic Induction and Alternating Current Book Back Questions

12th Standard EM

Reg.No. :
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Physics

Time : 00:45:00 Hrs
Total Marks : 30
5 x 1 = 5
1. Th e fl ux linked with a coil at any instant t is given by $\Phi$B =10t2−50t+ 250 . The induced emf at t = 3s is

(a)

−190 V

(b)

−10 V

(c)

10 V

(d)

190 V

2. A circular coil with a cross-sectional area of 4 cm2 has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm2. The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?

(a)

7.54 μH

(b)

8.54 μH

(c)

9.54 μH

(d)

10.54 μH

3. An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf v = 10 sin 340 t. The power loss in AC circuit is

(a)

0.76 W

(b)

0.89 W

(c)

0.46 W

(d)

0.67 W

4. In an oscillating LC circuit, the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is

(a)

$\frac{Q}{2}$

(b)

$\frac{Q}{\sqrt3}$

(c)

$\frac{Q}{\sqrt2}$

(d)

Q

5. $\frac{20}{\pi^2}H$inductor is connected to a capacitor of capacitance C. The value of C in order to impart maximum power at 50 Hz is

(a)

50 μF

(b)

0.5 μF

(c)

500 μF

(d)

5 μF

6. 3 x 2 = 6
7. What is meant by electromagnetic induction?

8. What is meant by mutual induction?

9. What do you mean by resonant frequency?

10. 3 x 3 = 9
11. A circular antenna of area 3 m2 is installed at a place in Madurai. The plane of the area of antenna is inclined at 47o with the direction of Earth’s magnetic field. If the magnitude of Earth’s field at that place is 40773.9 nT find the magnetic flux linked with the antenna.

12. A straight conducting wire is dropped horizontally from a certain height with its length along east – west direction. Will an emf be induced in it? Justify your answer.

13. A conducting rod of length 0.5 m falls freely from the top of a building of height 7.2 m at a place in Chennai where the horizontal component of Earth’s magnetic field is 40378.7 nT. If the length of the rod is perpendicular to Earth’s horizontal magnetic field, find the emf induced across the conductor when the rod is about to touch the ground. [Take g = 10 m s-2]

14. 2 x 5 = 10
15. An inverter is common electrical device which we use in our homes. When there is no power in our house, inverter gives AC power to run a few electronic appliances like fan or light. An inverter has inbuilt step-up transformer which converts 12 V AC to 240 V AC. The primary coil has 100 turns and the inverter delivers 50 mA to the external circuit. Find the number of turns in the secondary and the primary current.

16. A square coil of side 30 cm with 500 turns is kept in a uniform magnetic field of 0.4 T. The plane of the coil is inclined at an angle of 300 to the field. Calculate the magnetic flux through the coil.