Model Paper 3 — Physics STD 12 Science — Question

Assertion : All the radioactive elements are ultimately converted in lead.

Reason     : All the elements above lead are unstable.

(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.

When two identical capacitors are in series have 3mF  capacitance and when parallel 12mF. What is the capacitance of each

(a) 6 μF

(b) 3 μF

(c) 12 μF

(d) 9 μF

When a resistor of 11 W is connected in series with an electric cell, the current flowing in it is 0.5 A.  Instead, when a resistor of 5 W is connected to the same electric cell in series, the current increases by 0.4 A. The internal resistance of the cell is

(a)  1.5 W

(b) 2 W

(c)  2.5 W

(d) 3.5 W

The bond, that exists in a semiconductor is:

The work function of metal is 1 eV. Light of wavelength 3000 Å is incident on this metal surface. The velocity of emitted photo-electrons will be

(a) 10 m/sec

(b) 1  m/sec

(c)  m/sec

(d)  m/sec

Which of the following is an atom donor impurity?

A concave mirror of focal length 15 cm forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be

(a) 22.5 cm

(b) 7.5 cm

(c) 30 cm

(d) 45 cm

Time period for a magnet is T. If it is divided in four equal parts along its axis and perpendicular to its axis as shown then time period for each part will be

(a) 4T

(b) T/4

(c) T/2

(d) T

Which of the following about potential at a point due to a given point charge is true?
The potential at a point P due to a given point charge.