Worksheets7. Alternating Current
Total questions: 10
Worksheet time: 50mins
A bulb is connected first with dc and then ac of same voltage then it will shine brightly with
a.c
d.c
Brightness will be in ratio 1/(1.4).
Equally with both.
The variation of the instantaneous current (I) and the instantaneous emf (ε) in a circuit is as shown in the figure. Which of the following statements is correct?
The voltage lags behind the current by π/2.
The voltage leads the current by π/2
The voltage and the current are in phase.
The voltage leads the current by π.
The voltage of an ac source varies with time according to the equation
V = 100 sin (100π t) cos (100πt), where t is in seconds and V is in volts. Then
the peak voltage of the source is 100 V.
the peak voltage of the source is 50 V.
the peak voltage of the source is 2100 Volt
the frequency of the source is 50 Hz.
The vector diagram of current and voltage for a circuit is as shown. The components of the circuit will be
LCR
LR
LCR or LR
None
In an LR circuit, the inductive reactance is equal to the resistance R of the circuit. An emf E = E0 cos(ωt ) applied to the circuit. The power consumed in the circuit is
RE02
2RE02
4RE02
8RE02
L, C and R represent physical quantities inductance, capacitance and resistance, respectively. The combination representing dimension of frequency is
LC
(LC)2−1
(CL)2−1
LC
Power factor is maximum in an LCR series circuit when
XL=XC
R=0
XL =0
XC =0
Reactance of a capacitor of capacitance CμF for ac frequency π400 Hz is 25 Ω .
The value C is
50 μF
25 μF
100 μF
75 μF
A transformer is used to light a 100 W and 100 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately
30%
50%
90%
10%
A step-up transformer connected to a 220 V ac line is to supply 22 kV for a neon sign in secondary circuit. In primary circuit, a fuse wire is connected which is to blow when the current in the secondary circuit exceeds 10 mA. The turn ratio of the transformer is
50
100
150
200
