物理磁場 DSE、CE 選擇題

1.

Rectangular coil $PQRS$ is carrying a current flowing in clockwise direction. It is placed inside a uniform magnetic field pointing into the paper as shown in the figure above.

Rectangular coil PQRS in a uniform magnetic field into the paper, current clockwise

Which of the following statements are correct ?

(1)A magnetic force pointing to the right acts on

RS

.

(2)No magnetic force acts on

QR

.

(3)The resultant magnetic force acting on the coil is zero.

2.

In the figure below, the arrow shows the direction of the magnetic field at $Z$ due to a current-carrying solenoid.

Solenoid XY with a soft iron core, terminals P and Q, and an arrow at Z pointing to the right

The direction of current through the solenoid and the magnetic north pole of the solenoids are

	Direction of current	Magnetic north pole
	from $P$ to $Q$	$X$
	from $P$ to $Q$	$Y$
	from $Q$ to $P$	$X$
	from $Q$ to $P$	$Y$

3.

Wire PQ placed between two bar magnets with poles X and Z, experiencing an upward force F

A current carrying wire $Y$ is placed between two bar magnets as shown above. The wire experiences an upward force. Which of the following is/are the possible combination(s) of the direction of the current in $Y$ and the magnetic poles of $X$ and $Z$ ?

	pole $X$	current direction in $Y$	pole $Z$
(1)	N	from $P$ to $Q$	S
(2)	S	from $P$ to $Q$	N
(3)	N	from $Q$ to $P$	S

4.

Two parallel straight wires carrying equal upward currents, passing through a plane

The figure above shows two parallel straight wires carrying equal currents. Which of the following diagrams correctly shows the resultant magnetic field lines ?

Four magnetic field line patterns A to D for two wires with currents out of the plane

5.

A current carrying wire, perpendicular to the plane of the paper, is located at $P$ . $P$ is in the midway between two identical bar magnets with unknown polarities $X$ and $Y$ as shown in the figure. The current in the wire is flowing into the paper. The magnetic force $F$ acting on the wire is downward. Which of the following statements are correct ?

(1)

X

is a north pole and

Y

is a south pole.

(2)

F

is reversed if the current direction is reversed.

(3)

F

is larger if stronger bar magnets are used.

Wire at P between bar magnets X and Y, current into the paper, force F downward

6.

Two parallel wires each carrying current I in the same direction

Two parallel wires carry equal currents flowing in the same direction. Which of the following statements are correct ?

(1)The magnetic forces acting on the two wires form an action-reaction pair.

(2)The two wires attract each other.

(3)If the directions of the current in the two wires are both reversed, the wires will repel each other.

7.

Rectangular loop carrying current I in a uniform magnetic field to the right, free to rotate about the axis PQ, with an observer viewing from below

The above figure shows a rectangular loop of wire carrying a steady current $I$ . The rectangular loop can rotate freely about $PQ$ . If a uniform magnetic field to the right is applied, which of the following is correct ?

	Resultant magnetic force acting on the rectangular loop	Rotation of the rectangular loop about $PQ$
	non-zero	clockwise
	non-zero	anti-clockwise
	zero	clockwise
	zero	anti-clockwise

8.

A compass is placed inside an air-cored solenoid $XY$ which is connected to a d.c. supply with terminals $P$ , $Q$ as shown. If the end $X$ of the solenoid behaves as magnetic north pole, what are the polarity of the terminal $P$ and the direction in which the north pole of the compass needle points ? (The tip of the arrow represents the north pole of the compass needle.)

Air-cored solenoid XY with a compass at its centre, connected to terminals P and Q

	Polarity of $P$	Compass
	$+$	$\leftarrow$
	$+$	$\rightarrow$
	$-$	$\leftarrow$
	$-$	$\rightarrow$

9.

Home-made sound device: a coil above a plastic cup whose base has a fixed magnet, with signal input

The diagram shows a home-made device which can produce sound. In the device, a magnet is fixed to the base of a plastic cup. When a signal passes through the coil, the base vibrates to produce a sound. Which of the following methods can make the sound louder ?

(1)using a stronger magnet

(2)inserting a copper rod into the coil

(3)increasing the number of turns in the coil

10.

Flat circular current-carrying coil in the plane of the page, current entering and leaving at the bottom

Which of the following diagrams shows the magnetic field pattern formed around a flat circular current-carrying coil, in the plane as shown above ?

Four magnetic field line patterns A to D around the coil cross-section