Electric Charges and Fields — Physics STD 12 Science — Question

A person who is at rest as the charge moves by him will measure.

The process by which ac is converted into dc is known as:

Mark the correct statement

(a) Nuclei of different elements can have the same number of neutrons

(b) Every element has only two stable isotopes

(c) Only one isotope of each element is stable

(d) All isotopes of every element are radioactive

A metallic solid sphere is placed in a uniform electric field. The electric field lines follow the path(s) shown in figure as

The equivalent capacitance of three capacitors of capacitance   and   are connected in parallel is 12 units and product . When the capacitors   and   are connected in parallel, the equivalent capacitance is 6 units. Then the capacitance are

(a) 2, 3, 7

(b) 1.5, 2.5, 8

(c) 1, 5, 6

(d) 4, 2, 6

Which of following  can not be polarised

(a) Radio waves

(b) Ultraviolet rays

(c) Infrared rays

(d)  Ultrasonic waves

A primary cell has an e.m.f. of 1.5 volts, when short-circuited it gives a current of 3 amperes. The internal resistance of the cell is

(a) 4.5 ohm

(b) 2 ohm

(c) 0.5 ohm

(d) 1/4.5 ohm

Which of the following is not equal to watt

(a)

(b) Amp / Volt

(c) Amp × Volt

(d) Joule / sec

Assertion :   Photosensitivity of a metal is high if its work function is small.

Reason     : Work function =   where   is the threshold frequency.

(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 x-component of the resultant of several vectors:

1. Is equal to the sum of the x-components of the vectors.
2. May be smaller than the sum of the magnitudes of the vectors.
3. May be greater than the sum of the magnitudes of the vectors.
4. May be equal to the sum of the magnitudes of the vectors.