Electromagnetic Induction and Alternating Currents
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See all →- To an ac power supply of 220 V at 50 Hz, a resistor of 20 Ω, a capacitor of reactance 25 Ω and an inductor of reactance 45 Ω are connected in series. The corresponding current in the circuit and the phase angle between the current and the voltage is,… Answer: 2. 7.8 A and 45^° Key idea: in a series LCR circuit, Z=√(R²+(X_L-X_C)²) and tanφ=X_L-X_C/R . X_L-X_C=45-25=20\ Ω, Z=√(20²+20²)=20sqr... 1
- AB is a part of an electrical circuit (see figure). The potential difference "V_A - V_B", at the instant when current i = 2 A and is increasing at a rate of 1 amp / second is: Answer: 4. 10 volt Key idea: going from A to B, add the potential change across each element. The current flows from A to B and is increasin... 1
- A sheet is placed on a horizontal surface in front of a strong magnetic pole. A force is needed to :A. hold the sheet there if it is magnetic.B. hold the sheet there if it is non-magnetic.C. move the sheet away from the pole with uniform velocity if… Answer: 3. A and C only Key idea: A force is needed only if the magnetic pole exerts a force on the sheet. A: A magnetic sheet is attracted... 1
- A 10 μ F capacitor is connected to a 210 V, 50 Hz source as shown in figure. The peak current in the circuit is nearly (π=3.14): Answer: 3. 0.93 A Key idea: For a capacitor in an AC circuit the capacitive reactance is X_C=1/ω C and the peak current is I₀=V₀/X_C=V₀ω C ,... 1
- In an ideal transformer, the turns ratio is N_p/N_s=1/2. The ratio V_s : V_p is equal to (the symbols carry their usual meaning) : Answer: 3. 2 : 1 Key idea: For an ideal transformer V_s/V_p=N_s/N_p . Given N_p/N_s=1/2 , we get N_s/N_p=2 , so V_s:V_p=2:1 . It is a step-u... 1
- In the above diagram, a strong bar magnet is moving towards solenoid-2 from solenoid-1. The direction of induced current in solenoid-1 and that in solenoid-2, respectively, are through the directions: Answer: 2. AB and DC Key idea: Lenz's law: the induced current opposes the change in flux, so a solenoid end facing a moving magnet behaves... 1