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physics 2 ocr > G485 Definitions > Flashcards

G485 Definitions Flashcards

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1
Q

Define electric field strength

A

The electric field strength at a point is the force per unit charge exerted on a positive charge placed at that point

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2
Q

The electrical force experienced by an electron between parallel charged plates is given by the equation….

A

F = eV/d

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3
Q

State Coulomb’s law

A

Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them

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4
Q

The two units of electric field strength are…

A

NC-1 or Vm-1

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5
Q

We use Fleming’s LH rule

A

To predict the direction of the force on a charge carrying conductor placed in a magnetic field

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6
Q

We use Fleming’s RH rule

A

To predict the direction of the induced current in a conductor where there is relative movement between the conductor and a magnetic field.

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7
Q

The symbol B stands for

A

Magnetic flux density

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8
Q

The unit of magnetic flux density is

A

Tesla (T)

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9
Q

A charged particle moving at right angles to a uniform magnetic field will always travel…

A

In a circular path

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10
Q

For a charge q moving at right angles to magnetic field B what is the relationship between the momentum of the charged particle and the radius of its orbit?

A

The radius is directly proportional to the momentum (p=Ber)

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11
Q

Two devices which use r=mv/qB are

A

Mass spectrometers and particle accelerators

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12
Q

Magnetic Flux =

A

Magnetic flux density x Area

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13
Q

Magnetic flux linkage is defined as

A

The product of magnetic flux and the number of turns

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14
Q

Faraday’s law of electromagnetic induction is…

A

The magnitude of the induced e.m.f is proportional to the rate of change of magnetic flux linkage

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15
Q

Lenz’s law states….

A

That any induced current or e.m.f will be established in a direction so as to produce effects which oppose the change that is producing it.

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16
Q

A step up transformer

A

Increases voltage and reduces current

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17
Q

Define capacitance

A

Capacitance is the charge stored per unit of potential difference across it

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18
Q

The unit of capacitance is…

A

Farad (F)

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19
Q

An equivalent unit of the Farad is….

A

CV-1

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20
Q

The energy stored on a capacitor is given by

A

1/2QV

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21
Q

Decay is said to be exponential if….

A

A quantity reduces by a constant ratio in equal intervals of time

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22
Q

The time constant of a circuit is defined as….

A

The time taken for the current/charge/pd to fall to 1/e of its initial value

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23
Q

Time constant =

A

CR

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24
Q

Isotopes are…

A

Nuclei of the same element with different numbers of neutrons but the same number of protons

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25
Q

Hadrons are particles that

A

Are affected by the strong nuclear force

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26
Q

Two examples of hadrons are

A

Protons and Neutrons

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27
Q

Leptons are particles that

A

Are not affected by the strong nuclear force

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28
Q

An example of a lepton is

A

Electrons

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29
Q

Murray Gell Mann first proposed the idea of what in 1964?

A

Quarks

30
Q

Composition of a proton in terms of quarks is

A

u u d

31
Q

Composition of a neutron in terms of quarks is

A

u d d

32
Q

Binding energy is defined as

A

The minimum energy needed to pull a nucleus apart into its separate nucleons

33
Q

In a nuclear fission reactor which part slows down neutrons so that they are more likely to induce fission?

A

The moderator - usually graphite

34
Q

In a nuclear fission reactor which part absorbs neutrons in order to slow down the chain reaction?

A

The control rods - usually boron

35
Q

Name 3 coolants used in nuclear fission reactors

A

Water (PWR), Carbon dioxide (AGCR), Sodium

36
Q

An alpha particle consists of

A

2 neutrons and 2 protons

37
Q

A Beta - particle consists of

A

An electron

38
Q

A Beta + particle consists of

A

A positron

39
Q

Which particle associated with radioactive decay was discovered in 1956?

A

Neutrinos (and antineutrinos)

40
Q

How do the nucleon and proton numbers change during alpha decay

A

Nucleon number decreases by 4. Proton number decreases by 2

41
Q

How do the nucleon and proton numbers change during beta - decay

A

Nucleon number stays the same. Proton number increases by 1

42
Q

How do the nucleon and proton numbers change during beta + decay

A

Nucleon number stays the same. Proton number decreases by 1

43
Q

Define the decay constant

A

The probability that an individual nucleus will decay per unit time interval

44
Q

Define the activity of a radioactive source

A

The rate at which nuclei decay

45
Q

Define half life

A

The mean time taken for half of the nuclei in a sample to decay or
The mean time taken for the activity of a sample to reduce by half

46
Q

X rays are produced when…

A

Fast moving electrons are rapidly decelerated

47
Q

Three ways in which Xrays can be absorbed are…

A

Photoelectric effect, Compton scattering, Pair production

48
Q

Half thickness is defined as…

A

The thickness of absorber which reduces the intensity of an X ray beam by half

49
Q

Intensity is defined as

A

Power per unit cross sectional area

50
Q

Two methods of improving X ray images are

A

Image intensifiers and Contrast media

51
Q

Two advantages of CAT scans over X rays are…

A

They produce 3D images

They can distinguish between tissues of similar density

52
Q

The order of components in a gamma camera is

A

Collimator, Scintillator, Photocathode, Photomultiplier, Computer

53
Q

Radionuclides used in diagnostic medicine include…

A

Fluorine 18, Technetium 99, Iodine 123

54
Q

PET stands for …..

A

Positron Emission Tomography

55
Q

MRI stands for…

A

Magnetic Resonance Imaging

56
Q

`MRI uses which type of non ionising electromagnetic radiation?

A

Radio waves

57
Q

Advantages of MRI scans are….

A

No ionising radiation used
No moving mechanisms
Greater soft tissue contrast
Images easily computer enhanced in either 2D or 3D

58
Q

Disadvantages of MRI scans are

A

Cannot be used on patients with metal implants.

Pacemakers affected.

59
Q

Ultrasound is defined as ….

A

A sound with a frequency greater than 20,000Hz

60
Q

Ultrasound can be produced and detected by ….

A

A piezoelectric crystal transducer

61
Q

Acoustic impedance of a material =

A

density x speed of sound in material

62
Q

Gel is used in ultrasound scans in order to…

A

To ensure impedance matching to avoid the ultrasound being reflected at the air-skin boundary

63
Q

Doppler ultrasound is used…..

A

To monitor blood flow in the body

64
Q

Name 4 stages in the life cycle of massive stars that do not occur in the life cycle of average stars.

A

Super Red Giant
Supernova
Neutron Star
Black hole (only the most massive stars)

65
Q

The astronomical unit (AU) is

A

the average distance of the earth from the sun

~ 1.5 x 10(11) m

66
Q

The definition of a light year is….

A

The distance travelled by light in a vacuum in one year

67
Q

1 arc second =

A

1/3600 degrees

68
Q

The parsec is defined as ….

A

The distance that gives a parallax angle of 1 arc second

69
Q

State Hubble’s law

A

The speed of recession of a galaxy is directly proportional to its distance from earth

70
Q

The hot big bang model is also known as

A

The standard model of the universe

physics 2 ocr (15 decks)

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