Electromagnetism

Question 1

What is the Motor Effect?

Answer 1

A current-carrying conductor produces a magnetic field.

The Motor Effect is when the current-carrying conductor in an EXTERNAL magnetic field experiences a magnetic force due to the interaction between the external magnetic field and the current carrying conductor’s own magnetic field

Question 2

Why do current carrying conductors produce a magnetic field?

Answer 2

A moving electrical charge creates a magnetic field. This is just assumed knowledge, the very basis of electromagnetism.

A current is the rate of flow of electricity. Therefore, a current describes the flow of an abundance of electrical charges, which thus create a stronger magnetic field.

Question 3

What is the formula for magnetic force?

Answer 3

BIL sin(θ)

B = Magnetic Flux Density
I = Current
L = length of Conductor

Question 4

What is meant by magnetic flux density?

Answer 4

Magnetic flux is the measurement of how compact or tight the number of magnetic field lines are when they pass through a given area

Flux density is a measurement of the density of magnetic field lines.

Question 5

What even is density?

Answer 5

Density is mass per unit volume.

Measurement of how tightly a material is packed together

How ‘compact’ something is (closely tuck together)

Question 6

What is a conductor in electromagnetism?

Answer 6

A conductor is an object or material that allows the flow of electrical current through it

Question 7

What is Magnetic Flux?

Answer 7

Magnetic Flux is the number of magnetic field lines passing through a certain area

Question 8

What is magnetic flux density?

Answer 8

Magnetic Flux Density is how tight/compresssed the magnetic field lines are when passing through a given area.

For example, a low magnetic flux density means that the magnetic field lines are more spread apart in the given area.

Question 9

What is the symbol for Magnetic Flux Density in Formulas?

Answer 9

The magnetic flux density of a magnet is also called “B field” or “magnetic induction”. It is measured in tesla (SI unit)

Question 9

What is the formula for magnetic flux?

Answer 9

Φ = BA cos(θ)

Where,

Phi = Mangetic Flux Density x Area x cos(θ)

Question 10

What is the SI unti for magnetic flux?
(Hint, NOT MAGNETIC FLUX DENSITY)

Answer 10

Webers or Wb for short
Or Teslas per metre

Therefore, Wb or Tm^-1

Question 11

What does the symbol B stand for in electromagnetism formulas? What is the si units?

Answer 11

Magnetic flux density, measured in T

Therefore, Magnetic flux density is measured in Teslas

Question 12

In the formula for Magnetix Flux, what is the angle (θ) indicating?

Answer 12

Φ = BA cos(θ)

‘θ’ is the angle measured between the magnetic field lines and the normal of the conductor.

Therefore, construct a perpendicular (normal) to the conductor and measured the angle between this and the magnetic field lines)

Question 13

What is the symbol for magnetic flux?

Answer 13

Phi or Φ

Question 14

At what angle is the maximum magnetic flux experienced?

Answer 14

Maximum flux is experienced when the angle between the magnetic field lines and the normal to the plane is zero

(The plane is basically the surface of the conductor. Also this makes sense as cos 0 = 1)

Therefore, when the magnetic field lines are PERPENDICULAR to the plane, it experiences Maximum flux.

*Don’t get confused:

Max flux is when either:

• The magnetic field lines are perpendicular to the surface of the plane/conductor

OR

• When the angle between the magnetic field lines and the normal of the plane.conductor is 0 degrees

Therefore, it is the same thing - just a different way of expressing it. Both options mean the same, look at a visual diagram for support.

Question 15

What will happen when the magnetic field lines are in line with the direction of the normal?

Answer 15

This means that the angle between the magnetic field lines and the normal is zero. (Since it is both pointing the same way) Therefore, this means that maximum flux is produced.

Question 15

When is minimum magnetic flux produced?

Answer 15

Minimum magnetic flux is when the angle between the normal of the conductor/plane and the magnetic field lines is 90 degrees.

This makes sense as cos 90 = 0

Question 16

What are transformers?

Answer 16

Transformers are a pair of coils wound on the same metal core. (Typically copper or iron)The core is often shaped as a square loop with primary and secondary coils wound on opposite sides. The construction of a transformer allows the magnetic flux generated by a current changing in one coil to induce a current in the neighboring coil.

Therefore, the function of a transformer is to transfer electrical energy from one circuit into another through electrical induction. It does this by changing the voltage of level of an alternating current. (AC)

Question 17

Why are transformers used and why are they efficient/helpful?

Answer 17

Transformers are helpful because they distribute electricity efficiently over long distances and convert the voltage to fit one’s requirements. In summary, transformers help to efficiently manage and distribute electrical power across different circuits and voltage levels.

Question 18

Why do we use iron cores for a transformer?

Answer 18

We use an iron core to increase the strength of the magnetic field, that is produced in the primary coil

Question 19

Why are Transformers not 100% efficient? In an ideal scenario, they would be due to the Law of Conservation of Energy. But in real life, why not?

Answer 19

However, it is not 100% efficient, since transformers also lose energy through the form of electrical energy being converted into heat energy. This is due to the concepts of Eddy currents being restricted.

When the magnetic field in the core changes due to the alternating current passing through the windings, small circulating currents, known as eddy currents, are induced in the core material. These currents encounter resistance within the core material, leading to the conversion of electrical energy into heat. Eddy current losses can be minimized by using laminated cores, which reduce the paths available for these currents to flow.

Question 20

What is the definition of conventional current? Why is it not really used in physics and what is it supposed to be?

Answer 20

Conventional current is defined as the flow of positive charges. (Protons)
Therefore conventional current shows that current flows from the positive charge to the negative charge in a circuit/power supply.

However, electrical flow is the opposite direction of conventional current. It goes from the negative plate to the positive plate.

Question 21

What is alternating current? What is the difference between alternating current and direct current?

Answer 21

Alternating current is when the current flow switches back and forth. Therefore, it does not maintain a constant voltage and can range from positive to negative.

In DC (direct current) the electron current flows in one direction. Power sources with DC current often contain a constant voltage.

Question 22

Transformers use electromagnetic induction to transfer electrical current from one coil to another

Answer 22

True. A transformer is a device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage.

Question 23

Why is current inversely proportional to voltage in a transformer, when technically it should be proportional? (As shown in V = IR)

Answer 23

In a transformer, the voltage and current are inversely proportional due to the principle of conservation of energy. According to the transformer equation, V1 * I1 = V2 * I2, where V1 and I1 are the voltage and current on the primary side, and V2 and I2 are the voltage and current on the secondary side. When the voltage is stepped up on the secondary side, the current is stepped down proportionally to maintain the conservation of power. Similarly, when the voltage is stepped down, the current is stepped up. This relationship allows for efficient transfer of electrical energy between the primary and secondary coils of the transformer. Therefore, since P = VI and power is the rate of change in work (as well as Law of Conservation of energy), if we increase the voltage, then the current should decrease, in order to balance out the power in the transformer.

Question 24

In an ideal transformer, the input power should be equal to the output power. True or false?

Answer 24

True

Question 25

What is the relationship between the number of turns in the coil, current and voltage in a transformer?

Answer 25

The number of turns in a coil is directly proportional to the voltage in a transformer. Conversely, current is inversely proportional to the voltage, ONLY FOR TRANSFORMERS

Question 26

The B-field is the magnetic field. In what direction does the b-field naturally go in? (Hint: Whenever we solve any electromagnetism questions, we use conventional current)

Answer 26

The B-field naturally tends to go from the positive to the negative. Therefore, the B-field moves from North to South

Question 27

What does a change in magnetic flux produce?

Answer 27

A change in magnetic flux induces an EMF, an electromotive force (EMF is basically the potential difference/ voltage difference) The change in magnetic flux inducing an EMF is because of Faraday's Law.

Question 28

When and how are eddy currents produced?

Answer 28

Eddy currents are produced due to changes in the magnetic field. They are created when a conductor moves through a magnetic field or when the magnetic field around a stationary conductor varies. A change in magnetic flux density or change in direction of the magnetic field will produce an eddy current. Induced voltage/emf produces an eddy current

Question 29

What factors change the magnetic flux of a conductor?

Answer 29

Magnetic field strength, angle between conductor and magnetic field, area of conductor Just think about formula for magnetic flux, which is BAcos theta

Question 30

What is an eddy current? What causes it?

Answer 30

An eddy current is a loop of electrical current. Eddy current is the induced current from a metal plate as a result of Faraday and Lenz's Law. Eddy currents are only induced in conductors of large surface area, usually metal plates, cylindrical pipes made of conducting material.

Question 31

A magnet in a solenoid is stationary. Will it produce an induced emf? What will the ammeter say?

Answer 31

No, since there is no change in magnetic flux. The ammeter will read the same value as the original current, which is when there was no magnet going through the solenoid.

Question 32

Make sure to revise the general shit flashcards, they important too

Answer 32

ok

Question 33

Will there be an induced emf when a magnet is flowing inwards and outwards of a solenoid?

Answer 33

Yes as it produces a change in magnetic flux. Therefore, emf is induced and the ammeter readings will 'deflect' in one direction

Question 34

What is deflection?

Answer 34

The change of direction

Question 34

What is the difference between a galvanometer and an ammeter? Similarities?

Answer 34

They both measure current. However, an ammeter shows the magnitude of current whilst a galvanometer shows both magnitude and direction

Question 35

What does a change in magnetic flux result in? (In relation to emf and current?)

Answer 35

A change in magnetic flux induced EMF, according to Faraday's Law and this induced emf will cause current to flow. (note that this induced current will be in the opposite direction to the original current, since we have to consider Lenz's Law)

Question 36

Back emf is always opposite in direction to the emf produced by the DC motor

Answer 36

yes

Question 37

As back emf increases, the current decreases. Why?

Answer 37

Current decreases as back emf increases. This is due to Ohm's Law, which states V = IR and voltage is directly proportional to current. Basically, the net voltage is the emf - back emf. Therefore, as back emf increases, net voltage gets smaller and thus current also decreases.

Question 38

What is Lorentz force?

Answer 38

Lorentz force is the force that is exerted by a magnetic field on a moving electrical charge.

Question 39

What is the difference between F = BIL sin theta and F = qvB sin theta?

Answer 39

f = BIL sin theta is the force on a current in a magnetic field. However, F = qvB is the magnetic force on a moving charge.

Question 40

In F = qvB sin theta, what does the v stand for?

Answer 40

The 'v' stands for velocity, or otherwise the speed of the charge/object

Question 41

In which direction do the magnetic field lines go?

Answer 41

Magnetic field lines travel from the north to south direction. Think of electrons and protons. The electric field lines come out of a proton and go into an electron. The same thing applies here. Also think about conventional current and how it is positive to negative. Therefore, the B-field always goes from the north pole to the south pole, as it is positive to negative

Question 42

What does the ideal ammeter represent? What about the ideal voltmeter?

Answer 42

The ideal ammeter has zero electrical resistance. The ideal voltmeter has infinite electrical resistance.

Question 43

What is the Lorentz force?

Answer 43

The Lorentz force is the force experienced by a charged particle moving through an electric field and a magnetic field.

Question 44

What is the difference between F = qvB and F = BIL?

Answer 44

The force of magnetism = q(v*b) is defined for a point charge q moving in the magnetic field b with a velocity v. On the other hand, the force = ILB , it is the force of magnetism on a current carrying straight rod of length l, carrying a current I in magnetic field b.

Question 45

The formula sheet says sin theta for all angle formulas. What is the intuition behind maximum and minimum?

Answer 45

Maximum is when the angle is perpendicular. Therefore, cos 90 = 0 so this would be a minimum. However cos 0 is a maximum. For sin theta, it is the other way around.

Question 46

- A galvanometer has very low eletrical resistance. Therefore, ideal galvanometer should have zero resistance. (A galvanometer is an ammeter with both magnitude and direction of current - A voltmeter has electrical resistance, which means that an ‘ideal’ voltmeter would have infinite resistance - An ammeter has very low electrical resistance. Therefore, an ‘ideal’ ammeter would have zero resistance

Answer 46

true

Question 47

Transformers only work in AC motors, since change in current cannot be induced in DC motors, as it flows through only one direction. The transformer needs an alternating current to create a changing magnetic field, which can only happen if the AC source is grounded.

Answer 47

Yeah

Question 48

The faster a motor spins, the lower the current is

Answer 48

Facts

Question 49

Back emf is only for DC motors

Answer 49

Remember that