Important Questions For Practice
1. What is the magnitude of magnetic force per unit length on a wire carrying a current of 8A and making an angle of 30┬░ with the direction of a uniform magnetic field of 0.15T?
2. A straight wire of mass 200g and length 1.5 m carries a current of 2A. It is suspended in mid-air by a uniform horizontal magnetic field B. What is the magnitude of the magnetic field?
3. In a series CтАУR circuit, applied voltage is V = 110 sin 314t volt. What is the (i) The peak voltage (ii) Average voltage over half cycle?
4. A power transmission line feeds input power at 2400 V to a step down ideal transformer having 4000 turns in its primary. What should be number of turns in its secondary to get power output at 240V?
5. A series CтАУR circuit consists of a capacitance 16 mF and resistance 8╬й. If the input a.c. voltage is (200 V, 50 Hz), calculate (i) voltage across capacitor and resistor. (ii) Phase by which voltage lags/leads current.
Questions From Board Papers
1. The self inductance of the motor of an electric fan is 10H. What should be the capacitance of the capacitor to which it should be connected in order to impart maximum power at 50Hz?
2. An applied Voltage signal consists of a superposition of DC Voltage and an AC Voltage of high frequency. The circuit consists of an inductor and a capacitor in series. Show that the DC signal will appear across C where as AC signal will appear across L.
3. A sinusoidal e.m.f. device operates at amplitude E0 and frequency v across a purely (1) resistive (2) capacitive (3) inductive circuit. If the frequency of driving source is increased. How would (a) amplitude E0 and (b) amplitude I0 increase, decrease or remain same in each case?
4. Write an expression for the force experienced by a charged particle moving in a uniform magnetic field B. With the help of diagram, explain the principle and working of a cyclotron. Show that cyclotron frequency does not depend on the speed of the particle.
5. If the current sensitivity of a moving coil galvanometer is increased by 20% and its resistance also increased by 50% then how will the voltage sensitivity of the galvanometer be affected?
Important Questions On 12th Physics Chapter 7
Supply voltage, V = 220 V,
Frequency, ╬╜ = 50 Hz
┬а
The rms value of current in the circuit is given as
I = V/R
= 220/100
= 2.20 A
┬а
Q2
┬а
Vrms voltage is given as:
V = Vo/тИЪ2
= 300/тИЪ2
= 212.1 V
┬а
Q3
It is true that in any ac circuit, the applied voltage is equal to the average sum of the instantaneous voltages across the series elements of the circuit. However, this is not true for rms voltage because voltages across different elements may not be in phase.
A capacitor is used in the primary circuit of an induction coil. This is because when the circuit is broken, a high induced voltage is used to charge the capacitor to avoid sparks.