Atoms — Physics STD 12 Science — Question

Which of the transitions in hydrogen atom emits a photon of lowest frequency  (n = quantum number)

(a) n = 2 to n = 1

(b) n = 4 to n = 3

(c) n = 3 to n = 1

(d) n = 4 to n = 2

A radioactive decay chain starts from and produces     by successive emissions. The emitted particles can be

(a) Two a-particles and one b-particle

(b) Three   particles

(c) One a particle and two   particles

(d) One a particle and two   particles

Two condensers of capacity 0.3 μF  and 0.6 μF  respectively are connected in series. The combination is connected across a potential of 6 volts . The ratio of energies stored by the condensers will be         

(a)

(b) 2

(c)

(d) 4

Total flux produced by a source of 1 cd is

(a)

(b) 8

(c) 4

(d)

A 10 V storage battery of negligible internal resistance is connected across a 50 Ω resistor. How much heat energy is produced in the resistor in 1 hour

(a) 7200 J

(b) 6200 J

(c) 5200 J

(d) 4200 J

A ray of light of intensity I is incident on a parallel glass-slab at a point A as shown in fig. It undergoes partial reflection and refraction. At each reflection 25% of incident energy is reflected. The rays AB and A'B' undergo interference. The ratio   is

(a) 4 : 1

(b) 8 : 1

(c) 7 : 1

(d) 49 : 1

A very long bar magnet is placed with its north pole coinciding with the centre of a circular loop carrying as electric current i. The magnetic field due to the magnet at a point on the periphery of the wire is B. The radius of the loop is a. The force on the wire is:

A parallel plate air capacitor has a capacitance of 100 μμF.  The plates are at a distance d apart. If a slab of thickness   t( t ≤ d) and dielectric constant 5 is introduced between the parallel plates, then the capacitance will be

(a) 50 μμF

(b) 100 μμF

(c) 200 μμF

(d) 500 μμF

Assertion  :  The drift velocity of electrons in a metallic wire will decrease, if the temperature of the wire is increased.

Reason      : On increasing temperature, conductivity of metallic wire decreases.

(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.