## Atomic Structure, Multiple Choice Questions

(i) The e/m ratio of cathode ray is ———- C/kg.

 (a) 1.76 × 1023 (b)1.76 × 1011 (c) 1.76 × 10-31 (d) 1.76 × 107

Correct Option (b)

(ii) ———— determined the charge on an electron.
 (a) Millikan (b) J.J Thomson (c) Chadwick (d) Moseley
Correct Option: (a)
(iii) Neutron was discovered by —————-
 (a) Chadwick (b)Goldstein (c)J.J Thomson (d)de Broglie
Correct Option: (a)
(iv) The energy associated with quantum of radiation is —————–
 (a)hν (b) nh/2π (c) 2hν (d) 1/2 × hν
Correct Option: (a)
Note: ν is the frequency of radiation.

(v) What will be the wave number of a radiation with λ = 2 × 108 nm?

 (a) 0.5 × 10-8 nm (b) 10 nm (c) 5 nm (d) 100 nm

Correct Option: (a)
Solution: Wave number = 1/λ = 1/(2×108 nm) = 1/2 × 10-8 nm = 0.5 × 10-8 nm

(vi) Which of the following is not electromagnetic in nature?

 (a) IR rays (b) X-rays (c) γ rays (d) cathode rays

Correct Option: (d)

Explanation: All electromagnetic radiations are in the range of frequencies of about 3 × 1026 Hz to 3 × 103 Hz. They are further divided into 7 regions containing γ-rays, X-rays, ul (ultra violet) rays, visible light, IR (infra-red), microwaves and radio waves. Cathode rays does not include them.

(vii) Frequency of a green light is 6 × 1014 Hz. Its wave length is ———

 a)      500 nm b)      5 nm c)       5000 nm d)      100 nm

Solution

c=fλ ⇒ λ = c/f ⇒ λ = (3×108)/(6×1014) ⇒ λ = 0.5×10-6 ⇒ λ = 500 × 10-9 m = 500 nm

(viii) If the mass of electron is reduced to half, the Rydberg’s constant …..

 (a) becomes half (b) becomes double (c) remains unchanged (d) becomes one fourth

Correct Option: (a)

(ix) Which of the following is the mathematical form of Moseley’s law:

 (a) √ν = b(z – a) (b) √ν = a(z – b) (c) √ν = a/b √z (d) √ν = b/z.z

Correct Option: (b)

(x) For which of the following species, Bohr’s theory does not apply?

 (a) H (b) H+ (c) He+ (d) Li++

Correct Option: (b)

(xi) Which of the following set of four quantum numbers is correct for an electron in K-shell?

 (a) n =1, ℓ = 0, m =0, s = +1/2 (b) n = 2, ℓ = 1, m = 0, s = +1/2 (c) n = 1, ℓ = 1, m = 0, s = -1/2 (d) n = 2, ℓ = 2, m = +2, s = +1/2

Correct Option: (a)

(xii) The splitting of spectral line in the presence of magnetic field is called …..

 (a) Stark effect (b) Zeeman effect (c) Uncertainty Principle (d) Hund’s rule

Correct Option; (b)