4B2 Electric Fields and Magnetic Fields

Question 1

What is the SI unit for measuring the electric field?

Answer 1

Volt per meter (V/m)

The electric field (E) is defined as the force per unit charge, and 1 V/m equals 1 N/C.

Question 2

What is the SI unit for measuring the magnetic field?

Answer 2

Tesla (T)

One tesla is equal to one weber per square meter (Wb/m²)

Question 3

What did Hans Christian Oersted observe when he placed a compass near a current-carrying wire?

Answer 3

The compass needle deflected, revealing that electric currents produce magnetic fields.

This experiment marked the discovery of the link between electricity and magnetism.

Question 4

What is a common way to represent magnetic fields visually?

Answer 4

They are often represented by field lines, which show the direction and strength of the field.

Field lines are denser where the field is stronger.

Question 5

Define:

Electromagnetism

Answer 5

Interaction between particles and electric and magnetic fields.

It forms one of the four fundamental forces of nature.

Question 6

What is the relationship between electric and magnetic fields ?

Answer 6

They are interdependent and are components of electromagnetic waves, with changing electric fields generating magnetic fields and vice versa.

This dynamic relationship is described by Maxwell’s equations.

Question 7

True or False:

Electromagnetic waves consist of oscillating electric and magnetic fields perpendicular to each other.

Answer 7

True

These waves propagate through space without the need for a medium.

Question 8

How did Heinrich Hertz prove the existence of electromagnetic waves?

Answer 8

He generated and detected radio waves, showing that they exhibited reflection, refraction, and interference.

Hertz’s work validated Maxwell’s predictions about electromagnetic waves.

Question 9

What was the main finding of the Michelson-Morley experiment regarding electromagnetic waves?

Answer 9

It showed that the speed of light is constant regardless of the motion of the source or observer.

This experiment led to the dismissal of the “aether” theory and supported Maxwell’s equations.

Question 10

What are the four Maxwell’s equations described conceptually?

Answer 10

1. Gauss’s Law for electricity
2. Gauss’s Law for magnetism
3. Faraday’s Law of induction
4. Ampere-Maxwell Law

These laws form the foundation of classical electromagnetism.

Question 11

What does Gauss’s Law for electricity describe in electromagnetism?

Answer 11

It states that the electric flux through any closed surface is proportional to the total charge enclosed within it.

Gauss’s Law helps understand how electric fields originate from charges.

Question 12

True or False:

Gauss’s Law for Magnetism states that magnetic monopoles exist.

Answer 12

False

It states that magnetic monopoles do not exist and that the net magnetic flux through a closed surface is always zero.

Magnetic field lines form closed loops, unlike electric fields.

Question 13

Explain Faraday’s Law of electromagnetic induction.

Answer 13

It states that a changing magnetic field induces an electromotive force (EMF) in a circuit.

This principle underlies the operation of electric generators.

Question 14

What is the unit of induced EMF?

Answer 14

Volts (V)

Voltage is the potential difference across a conductor.

Question 15

What happens to the induced current if the magnetic flux remains constant?

Answer 15

No current is induced.

Only changes in flux induce currents.

Question 16

Fill in the blank:

The formula for Faraday’s law is _______.

Answer 16

Emf = -ΔΦ /Δt

Where Φ is magnetic flux.

Question 17

True or false:

The induced EMF depends on the rate of change of the magnetic flux.

Answer 17

True

Faster flux changes induce stronger EMFs.

Question 18

What did Faraday observe when he connected two coils on opposite sides of an iron ring?

Answer 18

He detected an induced current when the circuit was closed or opened, showing that a changing magnetic field induces an electric field.

This experiment confirmed the principle of mutual induction.

Question 19

Fill in the blank:

The faster the change in magnetic flux, the _______ the induced EMF.

Answer 19

greater

Rapid flux changes enhance induced voltage.

Question 20

What happens to the induced current when the magnetic field decreases?

Answer 20

The current flows to oppose the decrease.

This is illustrated by Lenz’s law in practical scenarios, such as a loop moving away from a magnet.

Question 21

Explain why Lenz’s Law supports the principle of energy conservation.

Answer 21

It ensures the induced current opposes the change, preventing energy from being created.

Without opposition, it would violate the first law of thermodynamics by creating energy.

Question 22

Why is Lenz’s Law important in electric generators?

Answer 22

It determines the direction of induced currents, ensuring efficient energy conversion.

Generators convert mechanical to electrical energy.

Question 23

What is the role of coils in maximizing induced EMF according to Faraday’s Law?

Answer 23

Coils increase the area through which flux changes, enhancing EMF.

This maximization principle is used in solenoids.

Question 24

True or false:

Faraday’s Law only applies to closed circuits.

Answer 24

False

It applies to open loops as well.

Question 25

# Fill in the blank: The **Ampere-Maxwell Law** relates a \_\_\_\_\_\_ \_\_\_\_\_ to the flow of electric current and changing electric fields.

Answer 25

magnetic field ## Footnote This law extended Ampere's original law by incorporating the effects of changing electric fields.

Question 26

How did Maxwell modify **Ampere's Law**?

Answer 26

He introduced the concept of **displacement current** to account for changing electric fields, completing the symmetry between electric and magnetic fields. ## Footnote This correction led to the development of Maxwell’s equations.

Question 27

# True or false: Magnetic fields are produced by **moving electric charges**.

Answer 27

True ## Footnote A current of moving electrons generates a magnetic field around the conductor, a principle used in electromagnets.

Question 28

# True or false: Ampere's Law can be used to calculate magnetic fields in **dynamic (changing) current** situations.

Answer 28

False ## Footnote Ampere's Law is only valid for steady currents.

Question 29

What is the formula for the magnetic field produced by a long straight wire according to **Ampere's Law**?

Answer 29

B = μ0I / (2πr) ## Footnote Where B is the magnetic field, μ0 is the permeability of free space, I is the electric current, and r is the distance from the wire.

Question 30

What is **magnetic permeability**?

Answer 30

The property that **describes the susceptibility of a material** to the influence of a magnetic field. ## Footnote It varies among different materials.

Question 31

# Fill in the blank: The **magnetic field** around a current-carrying wire forms \_\_\_\_\_\_\_ \_\_\_\_\_ around the wire.

Answer 31

circular loops ## Footnote The direction of the magnetic field is given by the **right-hand rule**.

Question 32

What did Ampere demonstrate by placing **two parallel current-carrying wires** near each other?

Answer 32

He observed that currents in the same direction attract each other, while currents in opposite directions repel. ## Footnote This experiment confirmed that magnetic forces exist between currents.

Question 33

What is a practical application of **Ampere’s Law** in technology?

Answer 33

It is used in **designing inductors** and **magnetic resonance imaging (MRI)** machines. ## Footnote These technologies rely on controlled magnetic fields.

Question 34

How does **Ampere's Law** apply in the **vacuum**?

Answer 34

The **displacement current** term ensures that magnetic fields exist even without free currents. ## Footnote This modification is essential for wave propagation in space.

Question 35

# True or false: A **steady electric** field generates a magnetic field.

Answer 35

False ## Footnote Only a changing electric field can generate a magnetic field.

Question 36

Explain how Lenz’s Law applies to a **falling magnet through a coil**.

Answer 36

A **current is induced** that opposes the magnet’s motion, slowing its fall. ## Footnote This slows down the magnet’s fall.

Question 37

What did **Arago and Fresnel** demonstrate about light in magnetic fields?

Answer 37

They showed that polarized light could rotate under the influence of a magnetic field (**Faraday Effect**). ## Footnote This suggested that magnetic fields could affect electromagnetic waves.

Question 38

What did Henry Rowland discover by **moving a charged plate**?

Answer 38

He demonstrated that **moving electric charges produce magnetic fields**, reinforcing the connection between electricity and magnetism. ## Footnote This supported the idea that magnetism results from moving charges.

Question 39

What is an **electromagnet**?

Answer 39

It consists of **coils of wire wrapped around an iron core** or other ferromagnetic material and a power source. ## Footnote It becomes a magnet only when current flows through the coils. The magnetic field is strengthened by the iron core.

Question 40

What factors affect the **strength** of an electromagnet?

Answer 40

* Number of loops * Presence and type of core * Amount of current ## Footnote More loops and higher current increase the magnetic field strength.

Question 41

# Defne: Mutual inductance

Answer 41

The ability of one current-carrying conductor to **induce a voltage** in another conductor through a mutual magnetic field. ## Footnote This phenomenon is the basis for the operation of transformers.

Question 42

What effect does a **current loop** experience when placed between **two magnetic poles**?

Answer 42

It experiences a **net force of zero** but may experience a torque. ## Footnote The torque tends to align the plane of the loop perpendicular to the magnetic field lines. This happens because opposite sides of the loop experience forces in opposite directions due to the magnetic field.

Question 43

# Define: Motional EMF

Answer 43

**Voltage induced in a conductor when it moves** through a magnetic field, cutting through magnetic flux lines. ## Footnote It is present when charges move in relation to an external magnetic field, changing the magnetic flux.

Question 44

What is the **formula** for calculating **motional EMF**?

Answer 44

EMF=B⋅L⋅v⋅sin(θ) ## Footnote Where B is magnetic field strength, L is length of the conductor, and v is velocity.

Question 45

A conductor moving **parallel to magnetic field** lines induces an EMF.

Answer 45

False ## Footnote Motion must cut across field lines for induction.

Question 46

# Fill in the blank: **Motional EMF** depends on the magnetic field strength, the velocity of the conductor, and the \_\_\_\_\_\_ of the conductor.

Answer 46

length ## Footnote Longer conductors induce higher EMFs when moving through a magnetic field.

Question 47

How does **increasing a conductor’s velocity** affect the induced EMF?

Answer 47

The EMF increases. ## Footnote Faster motion through a field enhances induction.

Question 48

What is a **practical example** of motional EMF?

Answer 48

Power generation in wind turbines. ## Footnote Rotating blades cut through magnetic fields to generate electricity.

Question 49

# Fill in the blank: **Motional EMF** is a result of the \_\_\_\_\_\_ force acting on charge carriers in a **moving conductor**.

Answer 49

Lorentz ## Footnote This force separates charges, creating voltage.

Question 50

Explain the effect of **conductor orientation** on motional EMF.

Answer 50

Maximum EMF occurs when the conductor moves perpendicular to the magnetic field. ## Footnote Parallel motion induces no EMF.

Question 51

# True or false: Increasing the **length of the conductor** increases the induced EMF.

Answer 51

True ## Footnote Longer paths for moving charges increase voltage.

Question 52

What role does motional EMF play in **railguns**?

Answer 52

It accelerates projectiles by inducing current in the rails. ## Footnote This current creates a powerful magnetic force.

Question 53

Why is motional **EMF** important in **electric motors**?

Answer 53

It provides feedback that regulates motor speed. ## Footnote This ensures efficient operation.

Question 54

What is the role of the **angle** between the conductor and magnetic field in **motional EMF**?

Answer 54

The induced EMF is maximum when the conductor moves **perpendicular** to the field. ## Footnote The angle directly affects induction efficiency.

Question 55

# Fill in the blank: In **motional EMF**, the conductor must move in such a way as to \_\_\_\_\_ the magnetic field lines.

Answer 55

cut ## Footnote Cutting field lines induces **voltage**.