物理 1983 年 DSE、CE 選擇題（第 3 頁）

21.

The atomic structure of isotopes of the same element differ from each other by having different numbers of

22.

Transverse wave with particles P at a crest, Q on the equilibrium line and R at a trough

A transverse wave is travelling steadily from left to right through a series of particles. At a certain instant the wave form is as shown in the figure. Which of the following statements about the particles is/are correct ?

(1)Particle

P

is moving down.

(2)Particle

Q

is moving up.

(3)Particle

R

is momentarily at rest.

23.

6 V battery with R1 in series with R2 and R3 in parallel

In the circuit shown, the resistances of $R_1$ , $R_2$ and $R_3$ are all equal to $2\ \Omega$ . The power dissipated by $R_2$ is

24.

When connected in series in an electric circuit, the power dissipated in two resistors $R_1$ and $R_2$ is in the ratio of $1:4$ . What will be the ratio of the power dissipated in $R_1$ and $R_2$ when they are connected in parallel ?

25.

Junction with 3 A and 2 A entering, 1 A leaving, and an ammeter A in the remaining wire

In the circuit shown, what is the current passing through the ammeter $A$ ?

26.

Circuit with ammeters A1, A2 and A3, two resistors, a battery and a switch S

In the above circuit, $A_1$ , $A_2$ and $A_3$ are ammeters of negligible internal resistance. What will happen to the readings of the ammeters if the switch $S$ is closed ?

Reading of $A_1$	Reading of $A_2$	Reading of $A_3$
decreases	increases	becomes zero
increases	decreases	becomes zero
unchanged	increases	becomes zero
unchanged	decreases	increases

27.

The resistance of a given conducting wire may be increased by

(1)decreasing the radius of the wire.

(2)increasing the length of the wire.

(3)winding the wire in the form of a coil.

28.

Bar magnet moving along the diameter of a metal ring, with the N pole nearer the ring and the magnet moving to the left

The figure shows a bar magnet moving along the diameter of a metal ring. Which of the following will happen ?

29.

Eight $100$ W lamps and one $1000$ W heater are all connected in parallel to a mains supply of $200$ V. Which of the following should be used ?

30.

The half-life of a radioactive substance is $8$ hours. Its initial mass is $3$ g. Find the amount of the radioactive substance remaining unchanged after $24$ hours.