4B2 Electric Fields and Magnetic Fields Flashcards
Describe the conceptual relationships between electric and magnetic fields
What is the SI unit for measuring the electric field?
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.
What is the SI unit for measuring the magnetic field?
Tesla (T)
One tesla is equal to one weber per square meter (Wb/m²)
What did Hans Christian Oersted observe when he placed a compass near a current-carrying wire?
The compass needle deflected, revealing that electric currents produce magnetic fields.
This experiment marked the discovery of the link between electricity and magnetism.
What is a common way to represent magnetic fields visually?
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.
Define:
Electromagnetism
Interaction between particles and electric and magnetic fields.
It forms one of the four fundamental forces of nature.
What is the relationship between electric and magnetic fields ?
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.
True or False:
Electromagnetic waves consist of oscillating electric and magnetic fields perpendicular to each other.
True
These waves propagate through space without the need for a medium.
How did Heinrich Hertz prove the existence of electromagnetic waves?
He generated and detected radio waves, showing that they exhibited reflection, refraction, and interference.
Hertz’s work validated Maxwell’s predictions about electromagnetic waves.
What was the main finding of the Michelson-Morley experiment regarding electromagnetic waves?
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.
What are the four Maxwell’s equations described conceptually?
- Gauss’s Law for electricity
- Gauss’s Law for magnetism
- Faraday’s Law of induction
- Ampere-Maxwell Law
These laws form the foundation of classical electromagnetism.
What does Gauss’s Law for electricity describe in electromagnetism?
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.
True or False:
Gauss’s Law for Magnetism states that magnetic monopoles exist.
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.
Explain Faraday’s Law of electromagnetic induction.
It states that a changing magnetic field induces an electromotive force (EMF) in a circuit.
This principle underlies the operation of electric generators.
What is the unit of induced EMF?
Volts (V)
Voltage is the potential difference across a conductor.
What happens to the induced current if the magnetic flux remains constant?
No current is induced.
Only changes in flux induce currents.
Fill in the blank:
The formula for Faraday’s law is _______.
Emf = -ΔΦ /Δt
Where Φ is magnetic flux.
True or false:
The induced EMF depends on the rate of change of the magnetic flux.
True
Faster flux changes induce stronger EMFs.
What did Faraday observe when he connected two coils on opposite sides of an iron ring?
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.
Fill in the blank:
The faster the change in magnetic flux, the _______ the induced EMF.
greater
Rapid flux changes enhance induced voltage.
What happens to the induced current when the magnetic field decreases?
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.
Explain why Lenz’s Law supports the principle of energy conservation.
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.
Why is Lenz’s Law important in electric generators?
It determines the direction of induced currents, ensuring efficient energy conversion.
Generators convert mechanical to electrical energy.
What is the role of coils in maximizing induced EMF according to Faraday’s Law?
Coils increase the area through which flux changes, enhancing EMF.
This maximization principle is used in solenoids.
True or false:
Faraday’s Law only applies to closed circuits.
False
It applies to open loops as well.
Fill in the blank:
The Ampere-Maxwell Law relates a ______ _____ to the flow of electric current and changing electric fields.
magnetic field
This law extended Ampere’s original law by incorporating the effects of changing electric fields.
How did Maxwell modify Ampere’s Law?
He introduced the concept of displacement current to account for changing electric fields, completing the symmetry between electric and magnetic fields.
This correction led to the development of Maxwell’s equations.
True or false:
Magnetic fields are produced by moving electric charges.
True
A current of moving electrons generates a magnetic field around the conductor, a principle used in electromagnets.
True or false:
Ampere’s Law can be used to calculate magnetic fields in dynamic (changing) current situations.
False
Ampere’s Law is only valid for steady currents.
What is the formula for the magnetic field produced by a long straight wire according to Ampere’s Law?
B = μ0I / (2πr)
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.
What is magnetic permeability?
The property that describes the susceptibility of a material to the influence of a magnetic field.
It varies among different materials.
Fill in the blank:
The magnetic field around a current-carrying wire forms _______ _____ around the wire.
circular loops
The direction of the magnetic field is given by the right-hand rule.
What did Ampere demonstrate by placing two parallel current-carrying wires near each other?
He observed that currents in the same direction attract each other, while currents in opposite directions repel.
This experiment confirmed that magnetic forces exist between currents.
What is a practical application of Ampere’s Law in technology?
It is used in designing inductors and magnetic resonance imaging (MRI) machines.
These technologies rely on controlled magnetic fields.
How does Ampere’s Law apply in the vacuum?
The displacement current term ensures that magnetic fields exist even without free currents.
This modification is essential for wave propagation in space.
True or false:
A steady electric field generates a magnetic field.
False
Only a changing electric field can generate a magnetic field.
Explain how Lenz’s Law applies to a falling magnet through a coil.
A current is induced that opposes the magnet’s motion, slowing its fall.
This slows down the magnet’s fall.
What did Arago and Fresnel demonstrate about light in magnetic fields?
They showed that polarized light could rotate under the influence of a magnetic field (Faraday Effect).
This suggested that magnetic fields could affect electromagnetic waves.
What did Henry Rowland discover by moving a charged plate?
He demonstrated that moving electric charges produce magnetic fields, reinforcing the connection between electricity and magnetism.
This supported the idea that magnetism results from moving charges.
What is an electromagnet?
It consists of coils of wire wrapped around an iron core or other ferromagnetic material and a power source.
It becomes a magnet only when current flows through the coils. The magnetic field is strengthened by the iron core.
What factors affect the strength of an electromagnet?
- Number of loops
- Presence and type of core
- Amount of current
More loops and higher current increase the magnetic field strength.
Defne:
Mutual inductance
The ability of one current-carrying conductor to induce a voltage in another conductor through a mutual magnetic field.
This phenomenon is the basis for the operation of transformers.
What effect does a current loop experience when placed between two magnetic poles?
It experiences a net force of zero but may experience a torque.
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.
Define:
Motional EMF
Voltage induced in a conductor when it moves through a magnetic field, cutting through magnetic flux lines.
It is present when charges move in relation to an external magnetic field, changing the magnetic flux.
What is the formula for calculating motional EMF?
EMF=B⋅L⋅v⋅sin(θ)
Where B is magnetic field strength, L is length of the conductor, and v is velocity.
A conductor moving parallel to magnetic field lines induces an EMF.
False
Motion must cut across field lines for induction.
Fill in the blank:
Motional EMF depends on the magnetic field strength, the velocity of the conductor, and the ______ of the conductor.
length
Longer conductors induce higher EMFs when moving through a magnetic field.
How does increasing a conductor’s velocity affect the induced EMF?
The EMF increases.
Faster motion through a field enhances induction.
What is a practical example of motional EMF?
Power generation in wind turbines.
Rotating blades cut through magnetic fields to generate electricity.
Fill in the blank:
Motional EMF is a result of the ______ force acting on charge carriers in a moving conductor.
Lorentz
This force separates charges, creating voltage.
Explain the effect of conductor orientation on motional EMF.
Maximum EMF occurs when the conductor moves perpendicular to the magnetic field.
Parallel motion induces no EMF.
True or false:
Increasing the length of the conductor increases the induced EMF.
True
Longer paths for moving charges increase voltage.
What role does motional EMF play in railguns?
It accelerates projectiles by inducing current in the rails.
This current creates a powerful magnetic force.
Why is motional EMF important in electric motors?
It provides feedback that regulates motor speed.
This ensures efficient operation.
What is the role of the angle between the conductor and magnetic field in motional EMF?
The induced EMF is maximum when the conductor moves perpendicular to the field.
The angle directly affects induction efficiency.
Fill in the blank:
In motional EMF, the conductor must move in such a way as to _____ the magnetic field lines.
cut
Cutting field lines induces voltage.
