Question 4661:

A light energy \(E\) falls on a metal and the electrons with a maximum kinetic energy of \(0.2 \mathrm{eV}\) are \(C\) ejected. If the work function of the metal is \(0.3 \mathrm{eV}\), what is the value of \(E\) ?

A. \(0.10 \mathrm{eV}\)
B. \(0.06 \mathrm{eV}\)
C. \(0.50 \mathrm{eV}\)
D. \(1.50 \mathrm{eV}\)

Question 4662:

A nucleus is unstable if ____________

A. It has two or more isotopes
B. Its binding energy is not sufficient to hold nuclear particles together.
C. It is very light with very low density
D. It has no significant mass.

Question 4663:

A radioactive substance has a half life of 4 years. If its activity today is 200 dps, its activity in 8 years from today is ____________

A. \(50 \mathrm{dps}\)
B. \(25 \mathrm{dps}\)
C. \(20 \mathrm{dps}\)
D. \(10 \mathrm{dps}\)

Question 4664:

A substance has a half-life of \(3 \mathrm{~min}\). After \(6 \mathrm{~min}\), the count rate was observed to be 400 . What was its count rate at zero time?

A. 2400
B. 200
C. 1200
D. 1600

Question 4665:

A stone and a feather are dropped from the same height above earth surface. Ignoring resistance, which of the following is correct?

A. The feather will be blown away by the wind while the stone will drop steadily
B. The stone and feather will both reach the ground at the same time
C. The feather will reach the ground first
D. The stone will reach the ground first