A Geiger counter placed 1 meter from a point source of radiation registers 100 counts per minute. If the Geiger counter is moved closer, half-way to the source, the counting rate will be
A)25 counts/min.
B)50 counts/min.
C)100 counts/min.
D)200 counts/min.
E)400 counts/min.

Question

Quizplus · Accepted Answer

The counting rate will increase according to the inverse square law, which states that intensity (or in this case, counts per minute) is inversely proportional to the square of the distance. Halving the distance (from 1 meter to 0.5 meters) increases the counts by a factor of 4 (since $1/0.5^2 = 4$), making the new count 400 counts/min.

A Geiger Counter Placed 1 Meter from a Point Source