物理 1991 年 DSE、CE 選擇題（第 4 頁）

31.

Two light bulbs $A$ and $B$ of ratings ' $10$ W, $6$ V' and ' $5$ W, $6$ V' respectively are connected in series to a $6$ V battery. Which of the following is/are correct ?

(1)The resistance of

A

is smaller than that of

B

.

(2)The current through

A

is the same as that through

B

.

(3)

A

is brighter than

B

.

32.

Fused 200 V primary circuit, 10 V secondary with identical bulbs rated 40 W 10 V in parallel

In the above circuit diagram, the transformer is $100\%$ efficient. What is the maximum number of identical light bulbs, each of rating '40 W, 10 V' that can be connected in parallel across the secondary coil without blowing the fuse ? (Assume that the fuse will blow if the current flowing through it exceeds $15$ A.)

33.

Which of the following equations represent(s) possible nuclear reaction(s) ?

(1)

{}^{27}_{13}\mathrm{Al}+{}^{4}_{2}\mathrm{He}\to{}^{30}_{15}\mathrm{P}+\text{proton}

(2)

{}^{2}_{1}\mathrm{H}+{}^{3}_{1}\mathrm{H}\to{}^{4}_{2}\mathrm{He}+\text{neutron}

(3)

{}^{234}_{90}\mathrm{Th}\to{}^{234}_{91}\mathrm{Pa}+\beta\text{ particle}

34.

Graph of activity (Bq) against time (minute): exponential decay from 40 Bq at 0 to about 4 Bq at 100 minutes

The activity of a radioactive source is recorded on a graph as shown above. What is the half-life of the source ?