Atoms — Physics STD 12 Science — Question

At a certain place, the horizontal component of earth's magnetic field is  times the vertical component. The angle of dip at that place is

(a) 60°

(b) 45°

(c) 90°

(d) 30°

If a magnet of length 10 cm and pole strength 40 A-m is placed at an angle of 45^o in an uniform induction field of intensity 2 × 10^–4 T, the couple acting on it is

(a) 0.5656 × 10–4 N-m

(b) 0.5656 × 10–3N-m

(c) 0.656 × 10–4 N-m

(d) 0.656 × 10–5 N-m

The width of forbidden energy gap in the semiconductor is approximately :

A radioactive sample with a half life of 1 month has the label : “Activity=2 micro curies on 1.8.1991.'' What will be its activity two months later

(a) 1.0 micro curies

(b) 0.5 micro curies

(c) 4 micro curies

(d) 8 micro curies

Light of wavelength 5000 Å falls on a sensitive plate with photoelectric work function of 1.9 eV. The kinetic energy of the photoelectron emitted will be

(a) 0.58 eV

(b) 2.48 eV

(c) 1.24 eV

(d) 1.16 eV

Thermionic emission from a heated filament varies with its temperature T as

(a)

(b) T

(c)

(d)

In a plano-convex lens the radius of curvature of the convex lens is 10 cm.  If the plane side is polished, then the focal length will be (Refractive index = 1.5)

(a) 10.5 cm

(b) 10 cm

(c) 5.5 cm

(d) 5 cm

An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following are true?

The number of protons in an atom of atomic number Z and mass number A is:

Assertion  :   The possibility of an electric bulb fusing is higher at the time of switching ON and OFF

Reason     : Inductive effects produce a surge at the time of switch ON and OFF

(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.