Electrostatics — Physics STD 12 Science — Question

When two bar magnets are coaxially placed at some distance from each other, then no torque works because:

In the connections shown in the adjoining figure, the equivalent capacity between A  and  B will be

(a) 10.8 μF

(b) 69 μF

(c) 15 μF

(d) 10 μF

A 4 mF capacitor, a resistance of 2.5 MW is in series with 12 V battery. Find the time after which the potential difference across the capacitor is 3 times the potential difference across the resistor. [Given ln(2)= 0.693]

(a) 13.86 s

(b) 6.93 s

(c) 7 s

(d) 14 s

As one considers orbits with higher values of n in a hydrogen atom, the electric potential energy of the atom?

Metallic solids are always opaque because

(a) Solids effect the incident light

(b) Incident light is readily absorbed by the free electron in a metal

(c) Incident light is scattered by solid molecules

(d) Energy band traps the incident light

A modified discharge tube is used as a ________:

The threshold wavelength for photoelectric effect of a metal is 6500 Å. The work function of the metal is approximately

(a) 2 eV

(b) 1 eV

(c) 0.1 eV

(d) 3 eV

A point source of light is placed in front of a plane mirror:

1. All the reflected rays meet at a point when produced backward.
2. Only the reflected rays close to the normal meet at a point when produced backward.
3. Only the reflected rays making a small angle with the mirror, meet at a point when produced backward.
4. Light of different colours make different images.

The ratio of de-Broglie wavelength of a a-particle to that of a proton being subjected to the same magnetic field so that the radii of their path are equal to each other assuming the field induction vector   is perpendicular to the velocity vectors of the a-particle and the proton is

(a) 1

(b)

(c)

(d) 2

Comment on the statement given below:
In self-inductionWhen the current in a coil is increasing, induced emf opposes it
When the current in a coil is decreasing, induced emf supports it