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Class 12 > PYQ PHYSICS > 2012 > Set 1

2012

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Q11
Mention the functions of any two of the following used in communication system:
(i) Transducer
(ii) Repeater
(iii) Transmitter .
(iv) Band pass Filter

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Q12
A cell of emf E and internal resistance r is connected to two external resistance R₁ and R₂ and a perfect ammeter. The current in the circuit is measured in four different situations
(i) without any external resistance in the circuit
(ii) with resistance R₁ only
(iii) with R₁ and R₂ in series combination
(iv) with R₁ and R₂ in parallel combination
The currents measured in the four cases are 0.42 A, 1.05 A, 1.4 A and 4.2 A, but not necessarily in the order. Identify the currents corresponding to the four cases mentioned above.

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Q13
The susceptibility of a magnetic material is -2.6 x 10⁻⁵ . Identify the type of magnetic material and state its two properties.

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Q14
Two identical circular wires P and Q each of radius R and carrying current I are kept in perpendicular planes such that they have a common center as shown in the figure. Find the magnitude and direction of the net magnetic field at the common centre of the two coils.
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Q15
When an ideal capacitor is charged by a d.c. battery, no current flows. However, when an a.c. source is used, the current flows continuously. How does one explain this based on the concept of displacement current ?

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Q16
Draw a plot showing the variation of
(i) electric field (E) and
(ii) electric potential (V) with distance r due to a point charge Q.

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Q17
Define self-inductance of a coil. Show that magnetic energy required to build up the current I in a coil of self inductance L is 1/2LI² given

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Q18
The current in the forward bias is known to be more (~ mA) than the current in the reverse bias (~ µA). What is the reason, then, to operate the photo diode in reverse bias ?

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Q19
A metallic rod of ‘L’ length is rotated with angular frequency of ‘ω’ with one end hinged at the center and the other end at the circumference of a circular metallic ring of radius L about an axis passing through the center and perpendicular to the plane of the ring. A constant and uniform magnetic field B parallel to the axis is present everywhere. Deduce the expression for the emf between the center and the metallic ring.

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Q20
The figure shows a series LCR circuit with L = 5.0 H, C = 80 µF, R = 40 Ω connected to a variable frequency 240 V source, calculate

(i) the angular frequency of the source which drives the circuit at resonance,
(ii) the current at the resonating frequency,
(iii) the rms potential drop across the inductor at resonance.

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