Science (English Medium) Class 12 - CBSE Important Questions for Physics

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.

State the principle of a step-up transformer. Explain, with the help of a labeled diagram, its working ?

Describe briefly and two energy losses, giving the reasons for their occurrence in actual transformers ?

Answer the following question.
In a series LCR circuit connected across an ac source of variable frequency, obtain the expression for its impedance and draw a plot showing its variation with frequency of the ac source. 

Answer the following question.
What is the phase difference between the voltages across the inductor and the capacitor at resonance in the LCR circuit? 

Answer the following question.
Draw the diagram of a device that is used to decrease high ac voltage into a low ac voltage and state its working principle. Write four sources of energy loss in this device.  

Answer the following question.
A small town with a demand of 1200 kW of electric power at 220 V is situated 20 km away from an electric plant generating power at 440 V. The resistance of the two wirelines carrying power is 0.5 Ω per km. The town gets the power from the line through a 4000-220 V step-down transformer at a sub-station in the town. Estimate the line power loss in the form of heat. 

The selectivity of a series LCR a.c. circuit is large, when ______.

A series combination of an inductor (L), capacitor (C) and a resistor (R) is connected across an ac source of emf of peak value E₀, and angular frequency (ω). Plot a graph to show variation of impedance of the circuit with angular frequency (ω).

Why are microwaves considered suitable for radar systems used in aircraft navigation?

Name the phenomenon which shows the quantum nature of electromagnetic radiation.

Gamma rays and radio waves travel with the same velocity in free space. Distinguish between them in terms of their origin and the main application.

Electromagnetic waves of wavelengths λ₁, λ₂ and λ₃ are used in a radar system, in water purifiers and in remote switches of TV, respectively.

1. Identify the electromagnetic waves.
2. Write one source for each of them.

Which one of the following electromagnetic radiation has the least wavelength?

Calculate the distance of an object of height h from a concave mirror of radius of curvature 20 cm, so as to obtain a real image of magnification 2. Find the location of the image also.

Draw a schematic ray diagram of a reflecting telescope showing how rays coming from a distant object are received at the eyepiece.

Plot a graph to show the variation of the angle of deviation as a function of the angle of incidence for light passing through a prism. Derive an expression for the refractive index of the prism in terms of angle of minimum deviation and angle of the prism.

You have learnt that plane and convex mirrors produce virtual images of objects. Can they produce real images under some circumstances? Explain.

A double convex lens is made of a glass of refractive index 1.55, with both faces of the same radius of curvature. Find the radius of curvature required, if the focal length is 20 cm.

What is a dispersion of light