Electric Charges and Fields — Physics STD 12 Science — Question

Assertion  : The positively charged nucleus of an atom has a radius of almost .

Reason      : In a-particle scattering experiment, the distance of closest approach for a-particles is

(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 the assertion and reason both are false.

The work done by the external force in bringing the charge q from infinity to a point is called as:

A current i passes through a wire of length l, radius of cross-section r and resistivity r. The rate of heat generation is

(a)

(b)

(c)

(d) ilρ/r

The magnetic flux linked with a vector area   in a uniform magnetic field  is

(a)

(b) AB

(c)

(d)

The relation between the number of free electrons in semiconductors (n) and its temperature (T) is

(a) n ∝

(b) n ∝ T

(c) n ∝

(d) n ∝

The image formed by a concave mirror:

1. Is always real.
2. Is always virtual.
3. Is certainly real if the object is virtual.
4. Is certainly virtual if the object is real.

Unit of induced emf is:

An electric wire is connected across a cell of e.m.f. E. The current  I is measured by an ammeter of resistance R. According to ohm's law

(a)

(b) E = IR

(c) E = R/I

(d) E = I/R

A charged particle moves in a uniform magnetic field. The velocity of the particle at some instant makes an acute angle with the magnetic field. The path of the particle will be:

When Neils Bohr shook hand with Werner Heisenberg, what kind of force they exerted?

1. Gravitational.
2. Electromagnetic.
3. Nuclear.
4. Weak.