# (Download) CBSE Class XII Physics (Alternating Current And Electrical Machines) Guess Paper : 2012 - Set - I

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## CBSE - NEW DELHI

## Guess Paper – 2012

## Class – XII

## Subject – Physics

## Alternating Current And Electrical Machines

**Question 1.** A Sinusoidal Voltage V=200 sin 314t is
Applied to a Resistor of 10
ohms Resistance. Calculate

(i) rms value of the voltage,

(ii) rms value of
the current and

(iii) power dissipated as heat in watts.

**Question 2.** An ideal inductor is in turn put across 220V, 50 Hz and 220V, 100 Hz
supplies. Will the current flowing through it in the two cases be the same or
different?

**Question 3.** What is the phase relationship between the current flowing and the
voltage applied in an ac circuit for a pure inductor?

**Question 4.**A virtual current of 4 A flows in a coil when it is connected in a
circuit having alternating current of frequency 50 Hz. Power consumed in the
circuit is 240 W. Calculate the inductance of the coil if the virtual p.d.
across it is 100 V.

**Question 5.** An ac source E = Eo Sinwt is applied across an inductor of inductance
L. Show mathematically that the current lags behind voltage by phase angle of
p/2.

**Question 6.** A capacitor is connected an
ac source. If the frequency of the source be increased, how does the current in
the capacitor is affected?

**Question 7. **A coil has an inductance of 1 henry.

(a) At what frequency will it
have a reactance of 3142 ohms?

(b) What should be the capacity of a capacitor,
which has the same reactance at that frequency?

**Question 8.** A 1mf capacitor is connected to a 220 V, 50 Hz ac source. Calculate
the rms value of the current through the circuit. Also find the peak value of
voltage across the capacitor.

**Question 9.** A capacitor C and a bulb B are connected in series to the ac mains as
shown. The bulb glows with some brightness. How will the glow of the bulb change
when a dielectric slab is introduced between the plates of the capcitor? Give
reason in support of your answer.

**Question 10.**An ac circuit consists of a 220 V 50 Hz supply connected across a 100 ohms resistance. What inductance should be connected in the circuit, in series with the resistance so that the current is reduced to half?