物理電磁感應 DSE、CE 選擇題

1.

Metal rod PQ moving to the right with speed v on metal rails in a uniform magnetic field into the paper, resistor connected across RS

A metal rod $PQ$ is moving with a uniform speed $v$ on a metal rail placed in a uniform magnetic field as shown in the figure above. A resistor is connected across $RS$ . Which of the following descriptions is/are correct ?

(1)Kinetic energy of the rod is converted into electrical energy.

(2)Current flows through the resistor from

S

to

R

.

(3)The induced current will be reversed if the rod moves in the opposite direction.

2.

Copper ring R above a solenoid carrying current I; points X (above the solenoid) and Y (centre of the solenoid); observer at O above

A copper ring $R$ is falling through a solenoid along the axis as shown. The plane of the ring is kept horizontal throughout. The solenoid is carrying a steady current $I$ . $Y$ is the centre of the solenoid. Which of the following combinations about the directions of the induced current in the ring (if any) at $X$ and at $Y$ as observed from $O$ is correct ?

	at $X$	at $Y$
	clockwise	clockwise
	clockwise	no current
	anticlockwise	clockwise
	anticlockwise	no current

3.

Bar magnet with ends X and Y moving left towards a solenoid with ends P and Q, dashed outline showing the earlier position, solenoid connected to a resistor

When a magnet is moving towards end $Q$ for a solenoid, it is found that a north pole is induced at end $Q$ . As shown in the figure above, the magnet passes through and moves away from the solenoid, what are the polarities of end $P$ of the solenoid and end $X$ of the magnet ?

	Polarity of end $P$	Polarity of end $X$
	S	S
	S	N
	N	S
	N	N

4.

Generator: coil between S and N poles with slip rings, brushes and a load PQ

The figure above shows the position of the coil in a generator at time $t=0$ . The current is taken to be positive when it flows from $P$ to $Q$ through the load. Which of the following graphs best represents the variation of current $I$ with time $t$ as the coil rotates ?

5.

Coil A connected to a cell and switch and coil B connected to an ammeter, both wound on a soft iron rod

An experiment about electromagnetism is designed as shown above. Coil $B$ has a greater number of turns than coil $A$ . Coil $B$ is connected to a sensitive ammeter. Which of the following statements is/are correct ?

(1)When the switch is closed, a steady current flows through the ammeter.

(2)At the moment when the switch is opened, a current flows through the ammeter momentarily.

(3)If the soft iron rod is replaced by a glass rod, the ammeter will have a greater deflection at the moment the switch is opened.

6.

Rectangular coil partly in a uniform magnetic field into the paper, pulled to the right

In the figure, a rectangular coil is pulled to the right with uniform speed in a uniform magnetic field pointing into the paper. Which of the following descriptions about the current induced in the coil and the magnetic force acting on the coil is correct ?

7.

Metal rod PQ moving to the right on a metal rail in a uniform magnetic field into the paper, with a galvanometer G in the circuit

Under an external force, a metal rod $PQ$ is moving with a uniform speed $v$ on a metal rail placed in a uniform magnetic field as shown above. Which of the following descriptions is/are correct ?

(1)Current flows through the galvanometer from

Q

to

R

.

(2)The metal rod will accelerate to right if the direction of the magnetic field is reversed.

(3)The pointer of the galvanometer will deflect to opposite direction if the direction of the magnetic field is reversed.

8.

Simple d.c. generator: coil between S and N poles with a split-ring commutator connected to a load, terminals X and Y

The above figure shows a simple structure of a d.c. generator. Which of the following statements is/are correct ?

(1)The current delivered to the load is constant.

(2)The current generated in the coil is alternating, but the current delivered to the load is unidirectional.

(3)The current flows through the load from

X

to

Y

.

9.

Bar magnet above a closed-loop copper coil placed on an electronic balance

An electronic balance reads $X$ when a closed-loop copper coil is placed on it as shown above. A bar magnet drops from certain height vertically above. Just before the magnet reaches the coil, the reading of the electronic balance is

10.

Rectangular coil at position A moving to position B across a uniform magnetic field pointing into the paper

A rectangular coil is moved with a uniform speed from position $A$ to position $B$ as shown above. Which of the following graphs represents the variation of the current induced in the coil with time ?