The Ultimate Electromagnetic Induction Quiz

1. When there is an EMF, the direction of the current will always be such that (the magnetic field caused by it) will try to oppose the change producing it. Whose law is this?

Faraday's Law

Lenz's Law

Maxwell's Law

Boltzmann's Law

Law of Conservation of Energy

1st Law of Thermodynamics

1st Law of Electrodynamics

Lenz's Law states that when there is an EMF, the direction of the current will always be such that the magnetic field caused by it will try to oppose the change producing it. This law is named after the Russian physicist Heinrich Lenz, who formulated it in 1834. It is an important principle in electromagnetism and is used to determine the direction of induced currents in electromagnetic devices such as generators and transformers.

Explanation

Lenz's Law states that when there is an EMF, the direction of the current will always be such that the magnetic field caused by it will try to oppose the change producing it. This law is named after the Russian physicist Heinrich Lenz, who formulated it in 1834. It is an important principle in electromagnetism and is used to determine the direction of induced currents in electromagnetic devices such as generators and transformers.

2. Which of the following does not necessarily increase the size of the EMF induced when magnetic north is placed into a coil

Moving the magnet faster

Increasing the number of coils of wire

Pulling the North out of the coil

Pulling the North out of the coil does not necessarily increase the size of the EMF induced. The size of the EMF induced is determined by factors such as the strength of the magnetic field, the speed at which the magnetic field changes, and the number of coils of wire. Pulling the North out of the coil does not directly affect any of these factors, so it does not necessarily increase the size of the induced EMF.

Explanation

Pulling the North out of the coil does not necessarily increase the size of the EMF induced. The size of the EMF induced is determined by factors such as the strength of the magnetic field, the speed at which the magnetic field changes, and the number of coils of wire. Pulling the North out of the coil does not directly affect any of these factors, so it does not necessarily increase the size of the induced EMF.

3. Lenz's Law on electromagnetic induction is directly associated with the conservation of

Mass

Charge

Momentum

Energy

Lenz's Law states that the direction of an induced electromotive force (emf) in a circuit is always such that it opposes the change in magnetic field that caused it. This law is derived from the principle of conservation of energy, which states that energy cannot be created or destroyed, only transferred or converted from one form to another. In the case of electromagnetic induction, when a change in magnetic field induces an emf, the law ensures that the induced current creates a magnetic field that opposes the change, thereby conserving the energy in the system. Hence, the correct answer is energy.

Explanation

Lenz's Law states that the direction of an induced electromotive force (emf) in a circuit is always such that it opposes the change in magnetic field that caused it. This law is derived from the principle of conservation of energy, which states that energy cannot be created or destroyed, only transferred or converted from one form to another. In the case of electromagnetic induction, when a change in magnetic field induces an emf, the law ensures that the induced current creates a magnetic field that opposes the change, thereby conserving the energy in the system. Hence, the correct answer is energy.

4. What is the basic argument which is needed to derive EMF= Blv

The electric force on the electron is greater than the magnetic force on the electron

The electric force on the electron is equal to the magnetic force on the electron

The electric force on the electron is less than the magnetic force on the electron

F=ma

The impulse of the electron is equal to its momentum change

The basic argument needed to derive EMF= Blv is that the electric force on the electron is equal to the magnetic force on the electron. This implies that the magnitude of the electric force and the magnitude of the magnetic force are equal, which leads to the equation EMF= Blv.

Explanation

The basic argument needed to derive EMF= Blv is that the electric force on the electron is equal to the magnetic force on the electron. This implies that the magnitude of the electric force and the magnitude of the magnetic force are equal, which leads to the equation EMF= Blv.

5. A magnet is placed into a coil. The induced EMF across the coil is 10mV. What would the EMF be if a coil replaced the coil with twice as many coils, and the passage of the magnet into the coil took twice as long.

0mV

5mV

10mV

20mV

40mV

If a coil with twice as many coils is used, the induced EMF across the coil would be the same as before, because the number of coils does not affect the magnitude of the induced EMF. Similarly, if the passage of the magnet into the coil took twice as long, it would not affect the induced EMF either. Therefore, the EMF would still be 10mV.

Explanation

If a coil with twice as many coils is used, the induced EMF across the coil would be the same as before, because the number of coils does not affect the magnitude of the induced EMF. Similarly, if the passage of the magnet into the coil took twice as long, it would not affect the induced EMF either. Therefore, the EMF would still be 10mV.

6. The North pole of a magnet is pushed into a coil, and a current is induced. Which of the following will NOT change the direction of induced current as measured by an ammeter?

Pulling the North end of the magnet out.

Pushing the south end of the magnet into the coil

Changing the polarity of the ammeter connected to the coil

Pushing the sound end of the magnet into the coil AND changing the polarity

When the north end of the magnet is pushed into the coil, a current is induced in the coil in a particular direction. Pulling the north end of the magnet out will also induce a current in the same direction. Changing the polarity of the ammeter connected to the coil will simply reverse the direction in which the current is measured. Pushing the south end of the magnet into the coil will induce a current in the opposite direction. However, pushing the south end of the magnet into the coil AND changing the polarity will not change the direction of the induced current, as the induced current will still be in the opposite direction.

Explanation

When the north end of the magnet is pushed into the coil, a current is induced in the coil in a particular direction. Pulling the north end of the magnet out will also induce a current in the same direction. Changing the polarity of the ammeter connected to the coil will simply reverse the direction in which the current is measured. Pushing the south end of the magnet into the coil will induce a current in the opposite direction. However, pushing the south end of the magnet into the coil AND changing the polarity will not change the direction of the induced current, as the induced current will still be in the opposite direction.

7. A magentic field points vertically upwards, a current-carrying wire carries current to the left. In which way will the force be on the current carrying wire?

UP

DOWN

To LEFT

TOWARDS you

AWAY from you.

To RIGHT

When a current-carrying wire is placed in a magnetic field, a force is exerted on the wire due to the interaction between the magnetic field and the current. According to the right-hand rule, if the magnetic field points vertically upwards and the current in the wire is to the left, the force on the wire will be directed away from you. This is because the magnetic field lines and the current direction are perpendicular to each other, resulting in a force that is perpendicular to both. Therefore, the correct answer is AWAY from you.

Explanation

When a current-carrying wire is placed in a magnetic field, a force is exerted on the wire due to the interaction between the magnetic field and the current. According to the right-hand rule, if the magnetic field points vertically upwards and the current in the wire is to the left, the force on the wire will be directed away from you. This is because the magnetic field lines and the current direction are perpendicular to each other, resulting in a force that is perpendicular to both. Therefore, the correct answer is AWAY from you.

8. What is the magnetic flux linked by a coil when the normal to the coil and the direction of the magnetic field lines are parallel?

Magnetic flux x area (and measured in Webers)

Magnetic flux x area (and measured in Teslas)

Magnetic flux density x area (and measured in Teslas)

Magnetic flux density x area (and measured in Webers)

Zero.

When the normal to the coil and the direction of the magnetic field lines are parallel, the correct answer is "Magnetic flux density x area (and measured in Webers)". This is because magnetic flux is defined as the product of the magnetic field strength (flux density) and the area perpendicular to the field. Since the normal to the coil and the direction of the magnetic field lines are parallel, the area is perpendicular to the field, and the magnetic flux is given by the product of the magnetic flux density and the area, measured in Webers.

Explanation

When the normal to the coil and the direction of the magnetic field lines are parallel, the correct answer is "Magnetic flux density x area (and measured in Webers)". This is because magnetic flux is defined as the product of the magnetic field strength (flux density) and the area perpendicular to the field. Since the normal to the coil and the direction of the magnetic field lines are parallel, the area is perpendicular to the field, and the magnetic flux is given by the product of the magnetic flux density and the area, measured in Webers.

9. The current in a coil varies at a constant rate of 2A in 50 minutes. A back e.m.f. of 4 V is induced in the coil. What is the self-inductance of the coil?

0.10 H

0.025 H

0.40 H

30 H

The self-inductance of a coil can be calculated using the formula L = ΔΦ/ΔI, where L is the self-inductance, ΔΦ is the change in magnetic flux, and ΔI is the change in current. In this case, the current is varying at a constant rate of 2A in 50 minutes, so the change in current is 2A. The back e.m.f. induced in the coil is 4V. Therefore, the self-inductance can be calculated as L = 4V/2A = 2Ω. Since 1H = 1Ω·s, the self-inductance is equal to 2Ω·s, which is equivalent to 0.10H.

Explanation

The self-inductance of a coil can be calculated using the formula L = ΔΦ/ΔI, where L is the self-inductance, ΔΦ is the change in magnetic flux, and ΔI is the change in current. In this case, the current is varying at a constant rate of 2A in 50 minutes, so the change in current is 2A. The back e.m.f. induced in the coil is 4V. Therefore, the self-inductance can be calculated as L = 4V/2A = 2Ω. Since 1H = 1Ω·s, the self-inductance is equal to 2Ω·s, which is equivalent to 0.10H.

10. If the magnetic flux density at the end of a long straight solenoid is B, the magnetic flux density at the center of the solenoid is

1/4 B

1/2 B

2B

0

The magnetic field inside a solenoid is uniform, meaning it has the same strength at every point. Since the solenoid is long and straight, the magnetic field lines are parallel and evenly distributed. The magnetic field at the center of the solenoid is half as strong as the magnetic field at the end of the solenoid. Therefore, the magnetic flux density at the center of the solenoid is 1/2 B.

Explanation

The magnetic field inside a solenoid is uniform, meaning it has the same strength at every point. Since the solenoid is long and straight, the magnetic field lines are parallel and evenly distributed. The magnetic field at the center of the solenoid is half as strong as the magnetic field at the end of the solenoid. Therefore, the magnetic flux density at the center of the solenoid is 1/2 B.