Electrostatic Potential and Capacitance — Physics STD 12 Science — Question

Assertion :   We can measure the potential barrier of a PN junction by putting a sensitive voltmeter across its terminals.

Reason     : The current through the PN junction is not same in forward and reversed bias.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If assertion is false but reason is true.

The binding energy per nucleon of helium is :

If all matters were made of electrically neutral particles such as neutrons:

1. There would be no force of friction.
2. There would be no tension in the string.
3. It would not be possible to sit on a chair.
4. The earth could not move around the sun.

Density of nucleus is about :

Magnetic dipole moment is a vector quantity directed from :

An X-ray tube is operated at 50 kV. The minimum wavelength produced is

(a) 0.5 Å

(b) 0.75 Å

(c) 0.25 Å

(d) 1 Å

Three charges are placed at the vertices of an equilateral triangle of side ‘a’ as shown in the following figure. The force experienced by the charge placed at the vertex A in a direction normal to BC is

(a)

(b)

(c) Zero

(d)

A double convex lens of focal length 20 cm is made of glass of refractive index 3 / 2. When placed completely in water (a,  its focal length will be

(a) 80 cm

(b) 15 cm

(c) 17.7 cm

(d) 22.5 cm

When the distance between the charged particles is halved, the force between them becomes

(a) One-fourth

(b) Half

(c) Double

(d) Four times