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Radiography Year 1 Diagnostic Physics Exam 1 RAD4046 > Electricity and magnetism > Flashcards

Electricity and magnetism Flashcards

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1
Q

How do you work out power?

A

Power=current X voltage

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2
Q

How do you work out I?

A

I means current

Current = power/voltage

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3
Q

What is the units for charge

A

Coulombs C

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4
Q

How to work out resistance?

A

Resistance= voltage/current

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5
Q

What is the units for resistance?

A

Ohms

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6
Q

How do you work out energy in circuits?

A

Energy= power X time (s)

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7
Q

What is current measured in?

A

Amps

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8
Q

What is a fuse and why is it important?

A

A fuse is a thin piece of wire which is designed to melt if the current flows for it is too high

A fault in a circuit might cause a large current

This may damage the device or start a fire

A fuse is to prevent this from happening

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9
Q

What is a magnet

A

Magnets have a magnetic field that exert a force onto another body that has magnetic properties

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10
Q

What are the types of magnets

A

Permanent magnet- always has a magnetic field

Temporary magnet- becomes magnetic under domain influence. Under influence of another magnet

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11
Q

What are the types of magnetic material?

A

Ferromagnetic- e.g iron, retains magnetism

Paramagnetic- e.g copper, low permeability
Gadolinium is used in MRI to improve images

Dramagnetic- No magnetism

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12
Q

What is domain theory?

A

Domains are areas in the magnet that align in order for the substance to be magnetic

So in substances that don’t have domains aligned they aren’t magnetic
-however some substances can have their domains with other magnets.

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13
Q

What affects the magnitude of force?

A

Propertional- strength of the magnets

Inversely proportional to the distance squared (the further away the weaker the force)

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14
Q

What are the units of magnetic field strength or magnetic flux density?

A

Measured in Gauss (G) (Not SI units)

Or Tesla (T) (SI units)

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15
Q

How many Gauss’s equal 1 Tesla

A

1 Tesla= 10,000 Gauss

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16
Q

How can magnetic fields arise?

A

Magnetic fields can arise due to current carrying conductors

As electrons flow a magnetic field will be generated around a electric wire

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17
Q

What is Lenz’s law?

And what can it cause?

A

The induced EMF is in the opposite direction to what caused it

This leads to power loses as the current generated is inhibited by the magnetic field as it opposes it

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18
Q

What does EMF stand for?

A

EMF- electromotive force is similar to potential difference

19
Q

What are the principals of magnetive?

A

Generator effect

Motor effect

20
Q

What are the electromagnetic laws?

A

Faraday’s laws

21
Q

What is the generator effect?

A

…..

Similar to motor effect execpt in reverse

22
Q

What is the motor effect?

Example

A

Coil of wire placed in a magnetic field, so when the current flows it creates a MF that opposes the first MF, which causes the coil to rotate. The rotation/movement can drive devices.

For Example, an induction motor spins the anode on the x-ray tube.

23
Q

What are the Faraday’s laws?

A

….

24
Q

What the influence of sharp objects on electric field?

And how to prevent it?

A

Charge collect around the surface of a object and sharp edges will have a higher concentration of charge.
This can result in electrical shock

To prevent this -earth them, no sharp edges

25
Q

What does current mean?

A

The number of electrons

26
Q

What’s another word for voltage?

A

Potential difference

27
Q

What does resistance mean and factors that effect it?

A

Resistance means that electrons are prevented from flowing

Heat increases resistance
Thin wires have more resistance
And thick wires have less resistance as electrons can flow more easily and heat up less quickly

28
Q

What does potential difference mean?

A 
Potential difference (voltage) is the driving force,
However current is the flow of electrons so in none circuits there is potential difference

But in circuits there is a flow of electrons

29
Q

What measure of current would you use in rad?

A

In rad milliamps (1mA=0.001Amp

30
Q

What is a semi- conductor

A

Semi-conductors permit the flow of electrons in one direction only (used to regulate flow in a circuit) e.g silicon

31
Q

What’s the units for power?

A

Watts

32
Q

What’s the units for energy?

A

Joules

33
Q

What is a solenoid?

A

Solenoid refers to a soft iron being used in the coil to strengthen the magnetic field

Current creates a magnetic field in the wire and the soft iron enhances it

34
Q

Why is electricity needed in an x-ray tube?

A

To cause electrons to be released from the cathode

To drive electrons to the anode for photon production

35
Q

What are the types of electrical current?

A 
Direct current (D.C)
Alternating current (A.C)
36
Q

What does direct current mean?

A

Flows in one direction does not change in direction when it reaches its peak

37
Q

What does alternating current mean?

A

Changes in direction but it reaches it’s peak

38
Q

What does Faraday’s law of electromagnetic induction mean?

A

When a conductor is placed in an changing magnetic field EMF is induced and if the conductor circuit is closed current is also induced.
Changing magnetic field induces alternating current.

39
Q

What device is used to get direct current from alternating current

A

Commutator (split ring) is used

40
Q

How does a step-up transformer work

A

If there is more coils in the secondary coil than the primary coil it steps up the voltage.

41
Q

How does a step-down transformer work?

A

If there is less coils in the secondary coil than the primary coil it steps down the voltage.

42
Q

What does a rectifier do?

A

Converts alternating current to direct current.

43
Q

How does a transformer work

A

It steps up or step downs the voltages
The changing magnetic field induces in the secondary coil
This is mutual induction

Radiography Year 1 Diagnostic Physics Exam 1 RAD4046 (16 decks)

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