物理 1998 年 DSE、CE 選擇題（第 4 頁）

31.

A $4$ V a.c. supply is stepped up to $20$ V by a transformer. If the current in the primary coil is $1$ A and the power loss of the transformer is $0.8$ W, find the current in the secondary coil.

32.

A nucleus $X$ emits a beta particle to form a daughter nucleus $Y$ . Which of the following statements is/are correct ?

(1)

X

and

Y

have the same number of neutrons.

(2)The number of protons in

X

is greater than that in

Y

by

1

.

(3)The total numbers of neutrons and protons in

X

and

Y

are equal.

33.

Which of the following diagrams correctly shows the directions in which $\alpha$ , $\beta$ and $\gamma$ radiations are deflected in a uniform electric field produced by two charged metal plates ?

Four diagrams A to D showing alpha, beta and gamma tracks between a positive plate on the left and a negative plate on the right

34.

Thickness gauge: a radioactive source above and a detector below an aluminium sheet moving between rollers

In a factory producing aluminium sheets of $1$ mm thickness, a thickness gauge is used to monitor the thickness of aluminium sheets. Which of the following states the correct radioactive source to be used in the thickness gauge and the reason behind ?

	Source	Reason
	$\alpha$	The amount of $\alpha$ particles passing through aluminium depends on its thickness.
	$\beta$	The amount of $\beta$ particles passing through aluminium depends on its thickness.
	$\beta$	$\beta$ particles are less harmful to human beings.
	$\gamma$	$\gamma$ radiation has the greatest penetrating power.