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Physics Flashcards

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1
Q

What are X-rays part of

A

The electromagnetic spectrum

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2
Q

Properties of X-rays

A

Very short wavelength
Cause ionisation
They affect a photographic film in the same way as light
They are absorbed by metal and bone
They are transmitted by soft tissue
Their wavelength is of the same order of magnitude as the diameter of an atom

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3
Q

What can X-rays be used for

A

Diagnosis and treatment of some medical conditions e.g. CT scans, bone fractures, dental problems and killing cancer cells

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4
Q

What are CCDs

A

Charge-coupled devices

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5
Q

What does the use of CCD’s allow

A

Images to be formed electronically

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6
Q

What must be taken when X-rays and CT scanners are in use

A

Precautions such as standing behind lead or lead glass shields

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7
Q

What can electronic systems can be used to produce

A

Ultrasound waves, which have a frequency higher than the upper limit of hearing for humans

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8
Q

What is the range of human hearing

A

20Hz to 20,000 Hz

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9
Q

When are ultrasound waves partially reflected

A

When they meet a boundary between two different media

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10
Q

How can you determine how far away a boundary is

A

Using the time taken for the reflections to reach a detector

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11
Q

What can ultrasound waves be used in

A

Medicine e.g. removal of kidney stones, pre-natal scanning

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12
Q

What is refraction

A

The change of direction of light as it passes through one medium to another

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13
Q

How does a lens from an image

A

By refracting light

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14
Q

What happens at the principal focus

A

In a convex or converging lens, parallel rays of light are brought to a focus

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15
Q

How do you work out the refractive index

A

sin i/sin r
i- angle of incidence
r - angle of refraction

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16
Q

What is the nature of an image defined by

A

Its size relative to the object, (magnified/diminished)
Whether it is upright or inverted relative to the object
Whether it is real or virtual

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17
Q

What are converging lens used as

A

Magnifying glass

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18
Q

What is the equation for magnification

A

Image height/ object height

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19
Q

Key features of the eye

A 
Retina 
Lens
Cornea 
Pupil/ iris 
Ciliary muscle 
Suspensory ligaments
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20
Q

What is long sight caused by

A

The eyeball being too short or the eye lens being unable to focus

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21
Q

What is short sight caused by

A

The eyeball being too long or the eye lens being unable to focus

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22
Q

What is the power of a lens given by

A

P = 1/f

P - power in dioptres, D
f - focal length in metres, m

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23
Q

What is the power of a converging lens

A

Positive

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24
Q

What is the power of a diverging lens

A

Negative

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25
Q

What is our range of vision

A

The eye can focus on objects between the near point (approx. 25 cm) and the far point (infinity)

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26
Q

What is the film in a camera or the CCDs in a digital camera equivalent to

A

The retina in the eye

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27
Q

What is the focal length of a lens determined by

A

The refractive index of the material from which the lens is made
The curvature of the two surfaces of the lens

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28
Q

For a given focal length, the greater the refractive index …

A

… The flatter the lens. This means that the lens can be manufactured thinner

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29
Q

How do you work out the refractive index

A

Refractive index = 1/sin c

c - critical angle

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30
Q

How can visible light be sent

A

Along optical fibres e.g. the endoscope for internal imaging

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31
Q

What is the laser an energy source for

A

Cutting
Cauterising
Burning
e.g. eye surgery

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32
Q

What is the centre of mass of an object

A

The point at which the mass of the object may be thought to be concentrated

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33
Q

If freely suspended, where will an object come to rest

A

With its centre of mass directly below the point of suspension

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34
Q

What is the centre of mass of a symmetrical object along

A

The axis of symmetry

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35
Q

How do you calculate a time period of a simple pendulum

A

T=1/f

T= time period 
f = frequency in hertz, Hz
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36
Q

What does the time period depend on

A

The length of a pendulum

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37
Q

What is the moment

A

The turning effect of a force

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38
Q

How do you calculate the size of a moment

A

M= F * d

M = moment in Newton-metres, Nm 
F= force in newtons, N
d = perpendicular distance from the line of action of the force to the pivot in metres, m
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39
Q

If an object is not turning, what must the total clockwise moment be balanced by

A

The total anti-clockwise moment about any pivot

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40
Q

What are levers

A

Force multipliers

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41
Q

What happens if the line of action of the weight of an object lies outside the base of the object

A

There will be a resultant moment and the body will tend to topple

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42
Q

What is virtually incompressible

A

A liquid

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43
Q

How is the pressure in a liquid transmitted

A

Equally in all directions

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44
Q

What enables hydraulic systems to be used as a force multiplier

A

The use of different cross-sectional area on the effort and load side of a hydraulic system

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45
Q

What is the pressure in different parts of a hydraulic system is given by

A

P= F/A

P - pressure in pascals, Pa
F - force in newtons, N
A - cross-sectional area in metres squared, m2

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46
Q

When an object moves in a circle, where does it continuously accelerate towards

A

The centre of the circle. This acceleration changes the direction of the body, not its speed

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47
Q

The centripetal force needed to make an object perform circular motion increases as:

A

The mass of the object increases
The speed of the object increases
The radius of the circle decreases

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48
Q

What happens when a current flows through a wire

A

A magnetic field is produced around the wire

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49
Q

The size of the force can be increased by:

A

Increasing the size of the magnetic field

Increasing the size of the current

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50
Q

When will the conductor not experience a force

A

If it is parallel to the magnetic field

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51
Q

When is the direction of the force reversed

A

If either the direction of the current or the direction of the magnetic field is reversed

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52
Q

If an electrical conductor ‘cuts’ through a magnetic field, what happens

A

A potential difference is induced across the ends of the conductor

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53
Q

What happens if a magnet is moved into a coil of wire

A

A potential difference is induced across the ends of the coil

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54
Q

In a step-up transformer the potential difference across the secondary coil is greater than …

A

… The potential difference across the primary coil

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55
Q

If transformers are assumed to be 100% efficient, what should the electrical power input equal

A

The electrical power output

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56
Q

What frequency do switch mode transformers operate at

A

A high frequency, often between 50kHz and 200kHz

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57
Q

Compared to traditional transformers working from a 50 Hz, switch mode transformers are :

A

Much lighter
Smaller
More efficient

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58
Q

When do switch mode transformers use very little power

A

When they are switched on but no load is applied

59
Q

What is a time period in terms of pendulums

A

Time taken for a full swing

60
Q

What is frequency in terms of pendulums

A

The number of swings in one second

61
Q

What is a swing of a pendulum

A

A complete oscillation

62
Q

The longer the pendulum …

A

The greater the time period
The lesser the frequency

(Time period and frequency have an inverse relationship)

63
Q

The shorter the pendulum …

A

The lesser the time period

The greater the frequency

64
Q

Where will force exerted on a liquid be transmitted to

A

Other points in the liquid

65
Q

What happens to wires when a high current passes through them

A

Heats up and a strong magnetic field

66
Q

If you reduce the current, what do you have to do to the voltage

A

Increase

67
Q

What device can be used to increase or decrease the voltage of the ac

A

Transformers

68
Q

Why is electricity generated as a.c. for the National Grid

A

Transformers don’t work with d.c.

69
Q

How do you generate induced current

A

Move a magnet into a coil

70
Q

What happens when you move a wire through a magnetic field

A

A current is induced

71
Q

How could you get a simple electric motor to spin the coil faster

A

Use a stronger magnet
Use a coil with more turns
Increase the voltage

72
Q

How could get a simple electric motor to make the coil spin in the opposite direction

A

Reverse the cell

Swap the magnets

73
Q

Where does magnetic field come out of

A

The North

74
Q

What is Fleming’s left-hand rule

A

Rule used to identify the direction of a force acting on a current-carrying wire in a magnetic field

75
Q

What is the thumb representing in Fleming’s left-hand rule

A

Direction of the force / motion

76
Q

What is the first finger representing in Fleming’s left-hand rule

A

Direction of the field

77
Q

What is the second finger representing in Fleming’s left-hand rule

A

Direction of current

78
Q

How to decrease the force acting on the wire

A

Use weaker magnets
Use less current
Rotation of magnets so the field is no longer perpendicular

79
Q

When is the strongest force created in the motor effect

A

When the field and wire (current) are at 90 degrees

80
Q

Why are transformers insulated

A

So that the current does not enter the core

81
Q

How do transformers work

A

Alternating current in the primary coil produces a changing magnetic field in the core. This induces an alternating potential difference across the secondary coil

82
Q

What is alternating current

A

One that reverses direction

5Hz of a.c. means that the direction is changed 5 times a second

83
Q

What is the centripetal force provided by

A

Tension
Friction
Gravity

84
Q

If the centre of mass is closer to the ground …

A

…The more stable it is

85
Q

The more points of contact to a surface …

A

… The more stable an object is

86
Q

In regular shapes, where is the centre of mass

A

Where the lines of symmetry cross. Therefore their line of action is inside the base each time. The shapes are in a state of balance or equilibrium

87
Q

How to find the centre of mass of an irregular shape

A

Hang a plumb line
Suspend card on the plumb line and draw a straight line
Suspend on a different point of the card and draw another line
Find where it crosses

88
Q

What is a plumb line

A

Mass on a string

89
Q

What does the strength of reflection of ultrasound waves tell you

A

Whether the substance is hard or soft

90
Q

What’s the speed of light

A

3*10^8

91
Q

What doesn’t happen when a light travels at the normal

A

Refraction

92
Q

What are converging lens

A

Convex lens

93
Q

What are diverging lens

A

Concave lens

94
Q

Focal point

A

Point at which light rays meet`

95
Q

How to find the focal length

A

By focussing a distant object on a piece of paper through the lens. The focal length is the distance between the centre of the lens and the image

96
Q

What lens is in our eye and drawn in ray diagrams

A

Converging

97
Q

Where do rays parallel to principal axis always meet

A

At the focal point/ principal focus

98
Q

When is the image real

A

When the rays meet at a point

99
Q

When is the image virtual

A

When the rays don’t meet at a point

100
Q

Centre axis

A

Line of symmetry through lens

101
Q

What image is produced when the object is at more than 2F

A

Real
Inverted
Diminished

102
Q

What image is produced when the object is at 2F

A

Real
Inverted
Same size

103
Q

What image is produced when the object is between 2F and F

A

Real
Inverted
Magnified

104
Q

What image is produced when the object is at F

A

No image is produced

105
Q

What image is produced when the object is less than F

A

Virtual
Upright
Magnified

106
Q

What image is produced with a diverging lens

A

Virtual
Diminished
Upright

107
Q

Why does the eye have to work at focussing on near objects

A

At rest the eye naturally focuses on distant objects

108
Q

What do the cornea and lens work together to do

A

Focus the image on the retina

109
Q

Where does most the refraction occur in the eye

A

Cornea

110
Q

What is ciliary muscles attached to

A

Suspensory ligaments

111
Q

How does the lens provide fine focus

A

By changing shape to provide for more or less refraction

112
Q

What s the lens made of

A

Elastic fibres and is attached to the suspensory ligaments

113
Q

What happens when the ciliary muscles are relaxed

A

Suspensory ligaments pull tight
Lens pull tight (thin)
Light doesn’t bend
You can focus on distant objects

114
Q

What happens when the ciliary muscles contract

A

Suspensory ligaments relax
Lens relax (fat)
Light bends
You can focus on near objects

115
Q

How to correct long sightedness

A

Using a convex lens to focus light rays before they reach the lens

116
Q

How to correct short sightedness

A

Using a concave lens

117
Q

Similarities between the eye and cameras

A

Shutter is similar to iris
Film/CCD is similar to retina
Aperture is similar to pupil
Both have lens

118
Q

When is the focal length shorter

A

When the lens has a higher refractive index

When the lens is more curved

119
Q

Where is the critical angle

A

Where total internal reflection takes place

120
Q

What does the ciliary muscles do

A

Pull the lens for focusing

121
Q

What does the cornea do

A

Lets light into the eye and begins focusing (refracting)

122
Q

What does the iris do

A

Control the amount of light entering the eye

123
Q

What does the lens do

A

Focus light onto the retina

124
Q

What does the optic nerve do

A

Send signals to the brain

125
Q

What does the pupil do

A

Let light through to the lens

126
Q

What does the retina do

A

Light sensitive layer - sends signals to the optic nerve

127
Q

What does the suspensory ligament do

A

Hold the lens in place

128
Q

What are CCD’s

A

Silicon chips about the size of a postage stamp, divided up into a grid of millions of identical pixels
They detect X-rays and produce electronic signals which are used to form high resolution images

129
Q

How do CT scans work

A

A patent is put inside the cylindrical scanner and an X-ray beam is fired and picked up by detectors on the opposite side
X-ray tube and detectors are rotated throughout
A computer interprets signals to form 2D images

130
Q

How are X-rays used to treat cancer

A

X-rays are focused on the tumour using a wide beam
Beam is rotated around patient with tumour at centre
This minimises the exposure of normal cells to radiation and reduces damage

131
Q

What can you not do with a virtual image

A

Project it onto a screen

132
Q

Examples of levers as force multipliers

A

Long sticks or bars
Wheelbarrows
Scissors

133
Q

When is there a resultant moment

A

When the total anti-clockwise moments do not match the total clockwise moments
The object will then move

134
Q

What is a magnetic field

A

A region where magnetic materials and wires carrying a current experience a force acting on them

135
Q

Solenoid

A

Coil of wire

136
Q

What is an electromagnet

A

A magnet whose magnetic field can be turned on and off with an electrical current

137
Q

What is the function of a split-ring commutator

A

Swap the contacts every half turn to keep the motor rotating in the same direction

138
Q

Electromagnetic induction

A

The creation of a potential difference across a conductor which is experiencing a change in magnetic field

139
Q

Which coil has more turns in a step up transformer

A

Secondary

140
Q

Which coil has more turns in a step down transformer

A

Primary

141
Q

Where does current flow from

A

The positive to the negative

142
Q

Where do electrons flow from

A

Negative to positive

143
Q

In which materials do light travel fastest

A

Ones with lower refractive index

144
Q

When is the only time total internal reflection can happen

A

When light is travelling from a more dense medium to a less dense one

Further Additional Science (3 decks)

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