Revision-Magnetic Effect of Electric Current

Which statement best describes the Right-Hand Thumb Rule for a current-carrying solenoid?

• Point your right thumb along the magnetic field; your curled fingers show current direction.

• Point your right thumb along the direction of current through the coils; your curled fingers indicate the magnetic field lines around the solenoid.

• Use your left hand: thumb shows current direction, fingers show magnetic field direction.

• Thumb points to the south pole and fingers curl toward the north pole.

A solenoid can act like which familiar magnetic object when current flows through it?

• An electrostatic plate

• A bar magnet

• A capacitor

• A diode

Looking at the two end-on coil sketches, the end where the current appears to circulate counterclockwise when viewed from that end corresponds to which pole?

• South pole

• North pole

• Either pole depending on core material

• No pole forms

Which change will increase the strength of the magnetic field inside a current-carrying solenoid most directly?

• Decrease the number of turns of the coil.

• Insert a soft iron core and/or increase the current through the coil.

• Reverse the battery terminals only.

• Place the solenoid near a bar magnet without changing current.

What is a compass needle?

• A device that measures electric current.

• A small pivoted magnet that aligns with the local magnetic field direction.

• A soft iron rod used as a core inside a solenoid.

• A coil that produces magnetic field when current flows.

When a compass needle is placed in a region with no magnetic field, what happens?

• It aligns pointing North-South.

• It rotates rapidly and settles randomly.

• It shows no preferred direction and does not align.

• It points toward the nearest electric charge.

If the magnitude of current in a straight conductor within a uniform magnetic field is doubled (with field and orientation unchanged), how does the magnetic force change?

• It halves.

• It remains the same.

• It doubles.

• It becomes zero.

What happens to the direction of magnetic force on a current-carrying conductor if the direction of current is reversed while the magnetic field is unchanged?

• The force direction stays the same.

• The force direction reverses.

• The force magnitude becomes infinite.

• The conductor experiences no force.

A bar magnet is divided into three labelled parts A, B, and C from left to right. Where is the magnetic field strength maximum and where is it minimum? Choose the best option.

• Maximum at A and C; minimum at B

• Maximum at B; minimum at A and C

• Maximum at A only; minimum at C only

• Equal at A, B, and C

In a diagram showing iron filings around a bar magnet labelled N (left) and S (right), what does the observed closed-curve alignment of filings demonstrate?

• Electric field lines form open curves

• Magnetic field lines are closed loops emerging from N and entering S

• Magnetism acts only at the poles and not in space around the magnet

• Iron filings repel each other and form circles