Science (English Medium) Class 12 - CBSE Important Questions

When an alternating voltage of 220V is applied across device X, a current of 0.25A flows which lags behind the applied voltage in phase by π/2 radian. If the same voltage is applied across another device Y, the same current flows but now it is in phase with the applied voltage.

1. Name the devices X and Y.
2. Calculate the current flowing in the circuit when the same voltage is applied across the series combination of X and Y.

A series LCR circuit is connected to an ac source. Using the phasor diagram, derive the expression for the impedance of the circuit.

What role dose infra-red radiation play in maintain the Earth’s warmth

What role dose infra-red radiation play in physical therapy?

Identify the part of the electromagnetic spectrum which is:

produced by bombarding a metal target by high speed electrons.

Write the range of frequency of these waves.

If the earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.

To which part of electromagnetic spectrum does a wave of frequency 3 × 10¹³ Hz belong?

To which part of the electromagnetic spectrum does a wave of frequency 5 × 10¹⁹ Hz belong?

To which part of the electromagnetic spectrum does a wave of frequency 5 × 10¹¹ Hz belong?

The small ozone layer on top of the stratosphere is crucial for human survival. Why?

The charging current for a capacitor is 0.25 A.  What is the displacement current across its plates?

Name the em waves which are used for the treatment of certain forms of cancer. Write their frequency range ?

Name the em waves which are produced during radioactive decay of a nucleus. Write their frequency range ?

Which part of electromagnetic spectrum is used in radar systems?

Write the range of the wavelength of the following electromagnetic radiations:
(a) Infrared rays
(b) Ultraviolet rays
(c) γ -rays

Write one use of each of the above.

Define the term "Intensity" in the photon picture of electromagnetic radiation. 

Identify the part of the electromagnetic spectrum used in (i) radar and (ii) eye surgery. Write their frequency range.

Identify the part of the electromagnetic spectrum used in
(i) radar and
(ii) eye surgery. Write their frequency range.

Name the radiation of the electromagnetic spectrum which is used for the following:

Radar and Give the frequency range.