Atoms — Physics STD 12 Science — Question

Mark the correct options:

1. A diode valve can be used as a rectifier.
2. A triode valve can be used as a rectifier.
3. A diode valve can be used as an amplifier.
4. A triode valve can be used as an amplifier.

Electric potential is equal to :

A parallel plate air capacitor is charged and then isolated. When a dielectric material is inserted between the plates of the capacitor, then which of the following does not change

(a) Electric field between the plates	(b) Potential difference across the plates
(c) Charge on the plates	(d) Energy stored in the capacitor

What physical quantities may X  and Y  represent ? (Y represents the first mentioned quantity)

(a) Pressure  v/s temperature of a given gas (constant volume)

(b) Kinetic energy v/s velocity of a particle

(c) Capacitance v/s charge to give a constant potential

(d) Potential v/s capacitance to give a constant charge

For a transistor the parameter b = 99. The value of the parameter a is

(a) 0.9

(b) 0.99

(c) 1

(d) 9

A modified discharge tube is used as a ________:

A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are joined together.  The power of the combination will be

(a) – 16 D

(b) + 16 D

(c) – 6 D

(d) + 6 D

A short bar magnet with its north pole facing north forms a neutral point at P in the horizontal plane. If the magnet is rotated by 90^o in the horizontal plane, the net magnetic induction at P is (Horizontal component of earth’s magnetic field = )

(a) 0

(b) 2

(c)

(d)

The magnetic field B with in the solenoid having n turns per metre length and carrying a current of i ampere is given by

(a)

(b)

(c) 4π

(d) ni

Which of the following series in the spectrum of hydrogen atom lies in the visible region of the electromagnetic spectrum?