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NECO Physics Past Questions & Answers - Page 55

271.

A metal has a work function of 3.0 eV. What is the threshold frequency of the metal when electrons are just liberated from the metal.(1 eV = 1.6 × 10-19J; h = 6.6 × 10-34Js)

A.

4.8 × 10-19Hz

B.

9.3 × 10-7Hz

C.

4.8 × 1014Hz

D.

7.3 × 1014Hz

E.

9.3 × 1014Hz

Correct answer is D

The work function (ϕ) of a metal is defined as:

ϕ=hf0

f0=ϕh

ϕ=3.0eV=3.0×1.6×1019

= 4.8×1019J

f0=4.8×10196.6×1034

= 0.727×1015s1

= 7.27×1014s1

272.

A lead-acid accumulator is used in preference to a dry battery in a car because

A.

a dry battery cannot supply the necessary high voltage

B.

a dry battery would not operate on a cold frosty morning

C.

the accumulator can give a bigger current and can be recharged

D.

the accumulator can supply a.c

E.

the chemicals used in a dry battery constitute a fire hazard.

Correct answer is C

No explanation has been provided for this answer.

273.

What gives rise to the line spectra observed in atoms?

A.

change of an electron from a higher to a lower energy level in the atom

B.

disturbed protons in the nucleus

C.

excitation of an electron in the atom

D.

kinetic energy of a moving atom

E.

potential energy of an electron inside an atom

Correct answer is A

No explanation has been provided for this answer.

275.

The wavelength of a stationary wave is 24.0cm. What is the distance between a node and the next antinodes?

A.

6.0cm

B.

12.0cm

C.

18.0cm

D.

24.0cm

E.

48.0cm

Correct answer is A

No explanation has been provided for this answer.