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

With the help of a diagram, show how a plane wave is reflected from a surface. Hence, verify the law of reflection.

A metallic plate exposed to white light emits electrons. For which of the following colours of light, the stopping potential will be maximum?

The relative magnetic permeability of a substance X is slightly less than unity and that of substance Y is slightly more than unity, then ______.

• Assertion (A): For the radiation of a frequency greater than the threshold frequency, the photoelectric current is proportional to the intensity of the radiation.
• Reason (R): Greater the number of energy quanta available, the greater the number of electrons absorbing the energy quanta and the greater the number of electrons coming out of the metal.

• Assertion (A): Putting the p-type semiconductor slab directly in physical contact with the n-type semiconductor slab cannot form the pn junction.
• Reason (R): The roughness at contact will be much more than inter atomic crystal spacing and continuous flow of charge carriers is not possible.

What is the effect of threshold frequency and stopping potential on increasing the frequency of the incident beam of light? Justify your answer.

Predict the direction of induced current in the situation described by the following figure.

Predict the direction of induced current in the situation described by the following figure.

Predict the direction of induced current in the situation described by the following figure.

Predict the direction of induced current in the situation described by the following figure.

Predict the direction of induced current in the situation described by the following figure.

Use Lenz’s law to determine the direction of induced current in the situation described by the figure.

A circular loop being deformed into a narrow straight wire.

Define 'quality factor' of resonance in a series LCR circuit. What is its SI unit?

Explain any two factors that justify the need of modulating a low-frequency signal.

A signal of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. What are the frequencies of the side bands produced?

In a series LCR circuit connected to an a.c. source of voltage v = v_msinωt, use phasor diagram to derive an expression for the current in the circuit. Hence, obtain the expression for the power dissipated in the circuit. Show that power dissipated at resonance is maximum

In a series LCR circuit, V_L = V_C ≠ V_R. What is the value of power factor?

A series LCR circuit is connected across an a.c. source of variable angular frequency 'ω'. Plot a graph showing variation of current 'i' as a function of 'ω' for two resistances R₁ and R₂ (R₁ > R₂).

Answer the following questions using this graph :

(a) In which case is the resonance sharper and why?

(b) In which case in the power dissipation more and why?

Draw a block diagram of a detector for AM signal and show, using necessary processes and the waveforms, how the original message signal is detected from the input AM wave.

A voltage V = V₀ sin ωt is applied to a series LCR circuit. Derive the expression for the average power dissipated over a cycle. Under what condition (i) no power is dissipated even though the current flows through the circuit, (ii) maximum power is dissipated in the circuit?