Science (English Medium) Class 12 - CBSE Question Bank Solutions for Physics

Write three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulated wave is obtained when a modulating signal is superimposed on a carrier wave.

The figure shows a series LCR circuit with L = 10.0 H, C = 40 μF, R = 60 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.

Why is electrostatic potential constant throughout the volume of the conductor and has the same value (as inside) on its surface?

Deduce the expression for the electrostatic energy stored in a capacitor of capacitance 'C' and having charge 'Q'.

How will the (i) energy stored and (ii) the electric field inside the capacitor be affected when it is completely filled with a dielectric material of dielectric constant K?

A series LCR circuit is connected to an ac source. Using the phasor diagram, derive the expression for the impedance of the circuit. Plot a graph to show the variation of current with frequency of the source, explaining the nature of its variation.

A hollow metal sphere of radius 10 cm is charged such that the potential on its surface is 5 V. What is the potential at the centre of the sphere?

Show that in an a.c. circuit containing a pure inductor, the voltage is ahead of current by π/2 in phase ?

Write two characteristics of a material used for making permanent magnets ?

Why is the core of an electromagnet made of ferromagnetic materials?

A series LCR circuit is connected to a source having voltage v = v_m sin ωt. Derive the expression for the instantaneous current I and its phase relationship to the applied voltage.

Obtain the condition for resonance to occur. Define ‘power factor’. State the conditions under which it is (i) maximum and (ii) minimum.

What type of wavefront will emerge from a (i) point source, and (ii) distance light source?

What is meant by term ‘modulation’? Draw a block diagram of a simple modulator for obtaining an AM signal.

 Derive an expression for the average power consumed in a series LCR circuit connected to a.c. source in which the phase difference between the voltage and the current in the circuit is Φ.

Draw a circuit diagram to study the input and output characteristics of an n-p-n transistor in its common emitter configuration. Draw the typical input and output characteristics.

Explain, with the help of a circuit diagram, the working of n-p-n transistor as a common emitter amplifier.

How is a zener diode fabricated so as to make it a special purpose diode? Draw I-V characteristics of zener diode and explain the significance of breakdown voltage.

Explain briefly, with the help of a circuit diagram, how a p-n junction diode works as a half wave rectifier.

Why should the material used for making permanent magnets have high coercivity?

Why is frequency modulation preferred over amplitude modulation for transmission of music?

Two sources are called coherent if they produce waves ______________ .