Physics Past Questions and Answers

I. All elements emit and absorb characteristic spectra. II. Spectral analysis is an important method of identifying environmental pollutants. III. The chemical composition of stars could be determined using spectral analysis. Which of the statements above are correct?

A I, II and III
B II and III only
C I and III only
D I and II only

Question 2887:

A metal has work function of 4.375 eV Calculate its threshold frequency. (h = 6.6 x 10^-34Js; 1eV = 1.6 x 10^-19J)

A 2.01 X 10¹⁵Hz
B 1.06x10¹⁵Hz
C 6.30 x 10¹⁴Hz
D 1.60 x 10¹⁴Hz

Question 2888:

The half-life of a radioactive substance is

A Its average life time
B One-half the value of its decay constant.
C The length of time needed by the substance to decay completely
D The length of time during which the activity of the substance reduces by 50%.

Question 2889:

The half-life of a radioactive element is 5 Calculate its decay constant

A 0.113s^-1
B 0.436 s^-1
C 0.139 s^-1
D 0.193 s^-1.

Question 2890:

A sheet of paper is placed in the path of the following radiations: I. Alpha particles II. Beta particles III. Gamma rays. Which of the radiations will pass through the sheet of paper?

A I only
B II only
C I and II only
D II and III only