Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions

An electron is accelerated from rest through a potential difference of 100 V. Find:

1. the wavelength associated with
2. the momentum and
3. the velocity required by the electron.

How mass defect is related to the stability of the nucleus?

Draw a labelled ray diagram showing the image formation by a refracting telescope. Define its magnifying power.

Which of the following graphs correctly represents the variation of a particle momentum with its associated de-Broglie wavelength?

• Assertion (A): The deflecting torque acting on a current-carrying loop is zero when its plane is perpendicular to the direction of the magnetic field.
• Reason (R): The deflecting torque acting on a loop of the magnetic moment `vecm` in a magnetic field `vecB` is given by the dot product of `vecm` and `vecB`.

How will the de-Broglie wavelength associated with an electron be affected when the velocity of the electron decreases? Justify your answer.

How will the de-Broglie wavelength associated with an electron be affected when the accelerating potential is increased? Justify your answer.

Draw a ray diagram for the formation of image of an object by an astronomical telescope, in normal adjustment. Obtain the expression for its magnifying power.

The magnifying power of an astronomical telescope in normal adjustment is 2.9 and the objective and the eyepiece are separated by a distance of 150 cm. Find the focal lengths of the two lenses.

A charge Q is placed at the centre of a cube. The electric flux through one of its faces is ______.

E, c and `v` represent the energy, velocity and frequency of a photon. Which of the following represents its wavelength?

In an astronomical telescope in normal adjustment, a straight black line of length L is drawn on the objective lens. The eyepiece forms a real image of this line whose length is 𝑙. What is the angular magnification of the telescope?

Write the underlying principle of a moving coil galvanometer.

State law of Malus.

Why does a galvanometer show a momentary deflection at the time of charging or discharging a capacitor? Write the necessary expression to explain this observation.

Obtain the expression for current sensitivity of moving coil galvanometer.

When an AC source is connected to an ideal capacitor, show that the average power supplied by the source over a complete cycle is zero

A bulb is connected in series with a variable capacitor and an AC source as shown. What happens to the brightness of the bulb when the key is plugged in and capacitance of the capacitor is gradually reduced?

A capacitor of capacitance C is charged fully by connecting it to a battery of emf E. It is then disconnected from the battery. If the separation between the plates of the capacitor is now doubled, how will the following change?

(i) charge stored by the capacitor.

(ii) Field strength between the plates.

(iii) Energy stored by the capacitor.

Justify your answer in each case.

A capacitor of capacitance ‘C’ is charged to ‘V’ volts by a battery. After some time the battery is disconnected and the distance between the plates is doubled. Now a slab of dielectric constant, 1 < k < 2, is introduced to fill the space between the plates. How will the following be affected? (a) The electric field between the plates of the capacitor Justify your answer by writing the necessary expressions.