Physics 11th Chap 12 : Topic 16 - Maryam Publications

Physics Chapter 12 : Topic 16

Seismometers and Electromagnetic Induction

1 / 25

The basic principle used by a seismometer to detect earthquakes is:

A) Electromagnetic induction

B) Nuclear induction

C) Thermal expansion

D) Electrostatic induction

2 / 25

In a seismometer, the coil is suspended by a spring mainly to:

A) Allow relative motion between the coil and magnet

B) Prevent electromagnetic induction

C) Increase the magnetic field strength

D) Keep the magnet permanently fixed to the coil

3 / 25

When an earthquake occurs, the rock on which a seismometer rests:

A) Vibrates and causes relative motion between magnet and coil

B) Remains stationary while the coil moves randomly

C) Changes the resistance of the coil only

D) Produces an electric current directly

4 / 25

If there is no relative motion between the magnet and the coil in a seismometer, the induced $\mathbf{e.m.f.}$ will be:

A) Minimum but non-zero

B) Zero

C) Infinite

D) Maximum

5 / 25

The magnet in a typical seismometer is usually attached to the:

A) Protective case only

B) Suspended spring system

C) External power supply

D) Earthquake recording paper

6 / 25

The induced $\mathbf{e.m.f}$ in the coil of a seismometer is produced because of a change in:

A) Mass of the magnet

B) Resistance of the coil

C) Temperature of the coil

D) Magnetic flux through the coil

7 / 25

The coil in a seismometer is suspended by a spring because the spring:

A) Increases the number of magnetic poles

B) Allows the coil to remain nearly stationary during ground vibrations

C) Converts electrical energy into mechanical energy

D) Eliminates magnetic flux changes

8 / 25

A stronger earthquake produces a larger induced $\mathbf{e.m.f.}$ in a seismometer because it causes:

A) A weaker magnetic field

B) Lower resistance of the coil

C) Greater displacement between magnet and coil

D) A decrease in coil turns

9 / 25

According to the SLO, the induced $\mathbf{e.m.f.}$ in the coil is directly proportional to:

A) Displacement associated with vibration

B) Temperature of the surroundings

C) Resistance of the coil

D) Mass of the magnet

10 / 25

If the displacement of the coil relative to the magnet is doubled, the induced $\mathbf{e.m.f.}$ will approximately:

A) Remain unchanged

B) Become double

C) Become half

D) Become zero

11 / 25

The protective case around a buried seismometer mainly helps to:

A) Protect the instrument from environmental damage

B) Increase the voltage produced

C) Stop all vibrations from reaching the coil

D) Remove the need for electromagnetic induction

12 / 25

A seismometer detects earthquake vibrations by converting:

A) Chemical energy into electrical energy

B) Mechanical energy into electrical signals

C) Heat energy into sound energy

D) Electrical energy into mechanical vibrations

13 / 25

The coil of a seismometer moves relative to the magnet because:

A) The magnet loses its magnetic properties.

B) The coil is electrically charged.

C) Both magnet and coil move with exactly the same velocity.

D) The frame moves with Earth while the suspended coil tends to resist motion.

14 / 25

Which change would increase the induced $\mathbf{e.m.f.}$ produced by a seismometer?

A) Stopping the coil movement completely

B) Removing the magnet

C) Increasing the displacement of vibration

D) Decreasing the displacement of vibration

15 / 25

The output signal from a seismometer represents:

A) The temperature below Earth’s surface

B) The colour of earthquake waves

C) The displacement and vibration strength of ground motion

D) The chemical composition of rocks

16 / 25

A seismometer is buried underground because:

A) It provides better contact with ground vibrations and protection.

B) Air vibrations are required for induction.

C) Underground rocks do not vibrate.

D) Magnetic fields only exist underground.

17 / 25

If the spring holding the coil becomes completely rigid, the seismometer will:

A) Produce a stronger signal

B) Increase magnetic flux automatically

C) Stop working effectively because relative motion decreases

D) Generate current without vibration

18 / 25

Which statement correctly describes the motion inside a seismometer during an earthquake?

A) The coil produces vibrations independently.

B) Both magnet and coil remain completely fixed.

C) The magnet remains fixed in space while the coil moves.

D) The magnet moves with the ground while the coil tends to remain stationary.

19 / 25

The direction of induced current in the seismometer coil is determined by:

A) Newton’s law

B) Lenz’s law

C) Ohm’s law

D) Boyle’s law

20 / 25

A seismometer with a more sensitive coil can detect weaker earthquakes because it:

A) Prevents all ground movement

B) Removes the need for a magnet

C) Stops electromagnetic induction

D) Produces a larger electrical response for small displacements

21 / 25

The main reason for using a coil and magnet arrangement in a seismometer is that:

A) Coils store earthquake energy.

B) Magnets stop seismic waves.

C) Earthquakes produce magnetic fields directly.

D) Mechanical vibrations can be measured as electrical signals.

22 / 25

If the earthquake causes no displacement between the coil and magnet, the recording device will show:

A) A constant electrical signal

B) Maximum earthquake intensity

C) Infinite voltage

D) No induced signal

23 / 25

A seismometer placed on a stronger vibrating surface produces a larger signal because:

A) The relative displacement increases

B) The magnet becomes heavier

C) The coil resistance increases

D) The spring disappears

24 / 25

Which combination correctly describes the operation of a seismometer?

A) Sound $\overset{\mathbf{\ \ \ \ \ \ \ \ \ }}{\rightarrow}$ electricity $\overset{\mathbf{\ \ \ \ \ \ \ \ \ }}{\rightarrow}$ heat

B) Pressure $\overset{\mathbf{\ \ \ \ \ \ \ \ \ }}{\rightarrow}$ magnetism $\overset{\mathbf{\ \ \ \ \ \ \ \ \ }}{\rightarrow}$ chemical energy

C) Heat $\overset{\mathbf{\ \ \ \ \ \ \ \ \ }}{\rightarrow}$ expansion $\overset{\mathbf{\ \ \ \ \ \ \ \ \ }}{\rightarrow}$ voltage

D) Vibration $\mathbf{\ }\overset{\mathbf{\ \ \ \ \ \ \ \ }}{\rightarrow}\mathbf{\ }$ relative motion $\mathbf{\ }\overset{\mathbf{\ \ \ \ \ \ \ \ }}{\rightarrow}\mathbf{\ }$ changing flux $\mathbf{\ }\overset{\mathbf{\ \ \ \ \ \ \ \ }}{\rightarrow}\mathbf{\ }$ induced $\mathbf{e.m.f}$

25 / 25

If the number of turns in the coil is increased, the induced $\mathbf{e.m.f.}$ will:

A) Remain completely unchanged

B) Increase because more flux changes occur

C) Decrease because resistance increases

D) Become zero

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