Important Questions For Practice
1. How will a diamagnetic, paramagnetic and a ferromagnetic material behave when kept in a non-uniform external magnetic field? Give two examples of each of these materials. Name two main characteristics of a ferromagnetic material which help us to decide suitability for making. (i) Permanent magnet (ii) Electromagnet.
2. Write the principle, working of moving coil galvanometer with the help of neat labelled diagram. What is the importance of radial field and phosphor bronze used in the construction of moving coil galvanometer?
3. Write two differences in each of resistance, reactance and impedance for an ac circuit. Derive an expression for power dissipated in series LCR circuit.
4. A uniform wire is bent into one turn circular loop and same wire is again bent in two turn circular loop. For the same current passed in both the cases compare the magnetic field induction at their centres.
[Answer: Increased 4 times]
5. A short bar magnet placed with its axis at 30┬░ with an external field 1000G experiences a torque of 0.02 Nm. (i) What is the magnetic moment of the magnet. (ii) What is the work done in turning it from its most stable equilibrium to most unstable equilibrium position? [Answer: (i) 0.4 Am2; (ii) 0.08 J]
Questions From Board Papers
1. A 1.5 ╬╝F capacitor is charged to 57V. The charging battery is then disconnected, and a 12 mH coil is connected in series with the capacitor so that LC Oscillations occur. What is the maximum current in the coil? Assume that the circuit has no resistance.
2. An electric bulb is connected in series with an inductor and an AC source. When switch is closed and after sometime an iron rod is inserted into the interior of inductor. How will the brightness of bulb be affected? Justify your answer.
3. How does mutual inductance of a pair of coils kept coaxially at a distance in air change when
(i) the distance between the coils is increased? (ii) an iron rod is kept between them?
4. In an inductor of inductance L, current passing is I0. Derive an expression for energy stored in it. In what forms is this energy stored?
5. In an LC circuit, resistance of the circuit is negligible. If time period of oscillation is T then:
(i) at what time is the energy stored completely electrical (ii) at what time is the energy stored completely magnetic (iii) at what time is the total energy shared equally between the inductor and capacitor.
Important Questions On 12th Physics Chapter 6
Wing span of jet plane, l = 25 m
EarthтАЩs magnetic field strength, B = 5.0 ├Ч 10^тИТ4 T
Angle of dip, ╬┤=30┬░
┬а
Vertical component of EarthтАЩs magnetic field,
BV = B sin ╬┤
= 5 ├Ч 10тИТ4 sin 30┬░
= 2.5 ├Ч 10^тИТ4 T
Voltage difference between the ends of the wing can be calculated as:
e = (BV) ├Ч l ├Ч v
= 2.5 ├Ч 10^тИТ4 ├Ч 25 ├Ч 500
= 3.125 V
Hence, the voltage difference developed between the ends of the wings is 3.125 V
┬а
Q2
Falling speed of the wire, v = 5.0 m/s
Magnetic field strength, B = 0.3 ├Ч 10тИТ4 Wb m^тИТ2
Emf induced in the wire,
e = Blv
= 0.3 ├ЧуАЦ10уАЧ^(-4) ├Ч 5 ├Ч 10
= 1.5 ├ЧуАЦ10уАЧ^(-3) V
Average induced emf = 0 V
Max current in the coil = 0.0603 A
Average power loss = 0.018 W
(Power comes from the external rotor)
Radius of the circular coil,
r = 8 cm = 0.08 m
Area of the coil,
A = ╧Аr2 = ╧А ├Ч (0.08)2 m^2
Number of turns on the coil,
N = 20
Angular speed,
╧Й = 50 rad/s
Magnetic field strength,
B = 3 ├Ч 10^тИТ2 T
Resistance of the loop,
R = 10 тДж
┬а
Maximum induced emf is given as:
e = N╧Й AB
= 20 ├Ч 50 ├Ч ╧А ├Ч (0.08)2 ├Ч 3 ├Ч 10^тИТ2
= 0.603 V
The maximum emf induced in the coil is 0.603 V.