Physics Flashcards
(144 cards)
1
Q
What are X-rays part of
A
The electromagnetic spectrum
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
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
4
Q
What are CCDs
A
Charge-coupled devices
5
Q
What does the use of CCD’s allow
A
Images to be formed electronically
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
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
8
Q
What is the range of human hearing
A
20Hz to 20,000 Hz
9
Q
When are ultrasound waves partially reflected
A
When they meet a boundary between two different media
10
Q
How can you determine how far away a boundary is
A
Using the time taken for the reflections to reach a detector
11
Q
What can ultrasound waves be used in
A
Medicine e.g. removal of kidney stones, pre-natal scanning
12
Q
What is refraction
A
The change of direction of light as it passes through one medium to another
13
Q
How does a lens from an image
A
By refracting light
14
Q
What happens at the principal focus
A
In a convex or converging lens, parallel rays of light are brought to a focus
15
Q
How do you work out the refractive index
A
sin i/sin r
i- angle of incidence
r - angle of refraction
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
17
Q
What are converging lens used as
A
Magnifying glass
18
Q
What is the equation for magnification
A
Image height/ object height
19
Q
Key features of the eye
A
Retina Lens Cornea Pupil/ iris Ciliary muscle Suspensory ligaments
20
Q
What is long sight caused by
A
The eyeball being too short or the eye lens being unable to focus
21
Q
What is short sight caused by
A
The eyeball being too long or the eye lens being unable to focus
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
23
Q
What is the power of a converging lens
A
Positive
24
Q
What is the power of a diverging lens
A
Negative
25
What is our range of vision
The eye can focus on objects between the near point (approx. 25 cm) and the far point (infinity)
26
What is the film in a camera or the CCDs in a digital camera equivalent to
The retina in the eye
27
What is the focal length of a lens determined by
The refractive index of the material from which the lens is made
The curvature of the two surfaces of the lens
28
For a given focal length, the greater the refractive index ...
... The flatter the lens. This means that the lens can be manufactured thinner
29
How do you work out the refractive index
Refractive index = 1/sin c
c - critical angle
30
How can visible light be sent
Along optical fibres e.g. the endoscope for internal imaging
31
What is the laser an energy source for
Cutting
Cauterising
Burning
e.g. eye surgery
32
What is the centre of mass of an object
The point at which the mass of the object may be thought to be concentrated
33
If freely suspended, where will an object come to rest
With its centre of mass directly below the point of suspension
34
What is the centre of mass of a symmetrical object along
The axis of symmetry
35
How do you calculate a time period of a simple pendulum
T=1/f
```
T= time period
f = frequency in hertz, Hz
```
36
What does the time period depend on
The length of a pendulum
37
What is the moment
The turning effect of a force
38
How do you calculate the size of a moment
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
```
39
If an object is not turning, what must the total clockwise moment be balanced by
The total anti-clockwise moment about any pivot
40
What are levers
Force multipliers
41
What happens if the line of action of the weight of an object lies outside the base of the object
There will be a resultant moment and the body will tend to topple
42
What is virtually incompressible
A liquid
43
How is the pressure in a liquid transmitted
Equally in all directions
44
What enables hydraulic systems to be used as a force multiplier
The use of different cross-sectional area on the effort and load side of a hydraulic system
45
What is the pressure in different parts of a hydraulic system is given by
P= F/A
P - pressure in pascals, Pa
F - force in newtons, N
A - cross-sectional area in metres squared, m2
46
When an object moves in a circle, where does it continuously accelerate towards
The centre of the circle. This acceleration changes the direction of the body, not its speed
47
The centripetal force needed to make an object perform circular motion increases as:
The mass of the object increases
The speed of the object increases
The radius of the circle decreases
48
What happens when a current flows through a wire
A magnetic field is produced around the wire
49
The size of the force can be increased by:
Increasing the size of the magnetic field
| Increasing the size of the current
50
When will the conductor not experience a force
If it is parallel to the magnetic field
51
When is the direction of the force reversed
If either the direction of the current or the direction of the magnetic field is reversed
52
If an electrical conductor 'cuts' through a magnetic field, what happens
A potential difference is induced across the ends of the conductor
53
What happens if a magnet is moved into a coil of wire
A potential difference is induced across the ends of the coil
54
In a step-up transformer the potential difference across the secondary coil is greater than ...
... The potential difference across the primary coil
55
If transformers are assumed to be 100% efficient, what should the electrical power input equal
The electrical power output
56
What frequency do switch mode transformers operate at
A high frequency, often between 50kHz and 200kHz
57
Compared to traditional transformers working from a 50 Hz, switch mode transformers are :
Much lighter
Smaller
More efficient
58
When do switch mode transformers use very little power
When they are switched on but no load is applied
59
What is a time period in terms of pendulums
Time taken for a full swing
60
What is frequency in terms of pendulums
The number of swings in one second
61
What is a swing of a pendulum
A complete oscillation
62
The longer the pendulum ...
The greater the time period
The lesser the frequency
(Time period and frequency have an inverse relationship)
63
The shorter the pendulum ...
The lesser the time period
| The greater the frequency
64
Where will force exerted on a liquid be transmitted to
Other points in the liquid
65
What happens to wires when a high current passes through them
Heats up and a strong magnetic field
66
If you reduce the current, what do you have to do to the voltage
Increase
67
What device can be used to increase or decrease the voltage of the ac
Transformers
68
Why is electricity generated as a.c. for the National Grid
Transformers don't work with d.c.
69
How do you generate induced current
Move a magnet into a coil
70
What happens when you move a wire through a magnetic field
A current is induced
71
How could you get a simple electric motor to spin the coil faster
Use a stronger magnet
Use a coil with more turns
Increase the voltage
72
How could get a simple electric motor to make the coil spin in the opposite direction
Reverse the cell
| Swap the magnets
73
Where does magnetic field come out of
The North
74
What is Fleming's left-hand rule
Rule used to identify the direction of a force acting on a current-carrying wire in a magnetic field
75
What is the thumb representing in Fleming's left-hand rule
Direction of the force / motion
76
What is the first finger representing in Fleming's left-hand rule
Direction of the field
77
What is the second finger representing in Fleming's left-hand rule
Direction of current
78
How to decrease the force acting on the wire
Use weaker magnets
Use less current
Rotation of magnets so the field is no longer perpendicular
79
When is the strongest force created in the motor effect
When the field and wire (current) are at 90 degrees
80
Why are transformers insulated
So that the current does not enter the core
81
How do transformers work
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
What is alternating current
One that reverses direction
| 5Hz of a.c. means that the direction is changed 5 times a second
83
What is the centripetal force provided by
Tension
Friction
Gravity
84
If the centre of mass is closer to the ground ...
...The more stable it is
85
The more points of contact to a surface ...
... The more stable an object is
86
In regular shapes, where is the centre of mass
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
How to find the centre of mass of an irregular shape
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
What is a plumb line
Mass on a string
89
What does the strength of reflection of ultrasound waves tell you
Whether the substance is hard or soft
90
What's the speed of light
3*10^8
91
What doesn't happen when a light travels at the normal
Refraction
92
What are converging lens
Convex lens
93
What are diverging lens
Concave lens
94
Focal point
Point at which light rays meet`
95
How to find the focal length
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
What lens is in our eye and drawn in ray diagrams
Converging
97
Where do rays parallel to principal axis always meet
At the focal point/ principal focus
98
When is the image real
When the rays meet at a point
99
When is the image virtual
When the rays don't meet at a point
100
Centre axis
Line of symmetry through lens
101
What image is produced when the object is at more than 2F
Real
Inverted
Diminished
102
What image is produced when the object is at 2F
Real
Inverted
Same size
103
What image is produced when the object is between 2F and F
Real
Inverted
Magnified
104
What image is produced when the object is at F
No image is produced
105
What image is produced when the object is less than F
Virtual
Upright
Magnified
106
What image is produced with a diverging lens
Virtual
Diminished
Upright
107
Why does the eye have to work at focussing on near objects
At rest the eye naturally focuses on distant objects
108
What do the cornea and lens work together to do
Focus the image on the retina
109
Where does most the refraction occur in the eye
Cornea
110
What is ciliary muscles attached to
Suspensory ligaments
111
How does the lens provide fine focus
By changing shape to provide for more or less refraction
112
What s the lens made of
Elastic fibres and is attached to the suspensory ligaments
113
What happens when the ciliary muscles are relaxed
Suspensory ligaments pull tight
Lens pull tight (thin)
Light doesn't bend
You can focus on distant objects
114
What happens when the ciliary muscles contract
Suspensory ligaments relax
Lens relax (fat)
Light bends
You can focus on near objects
115
How to correct long sightedness
Using a convex lens to focus light rays before they reach the lens
116
How to correct short sightedness
Using a concave lens
117
Similarities between the eye and cameras
Shutter is similar to iris
Film/CCD is similar to retina
Aperture is similar to pupil
Both have lens
118
When is the focal length shorter
When the lens has a higher refractive index
| When the lens is more curved
119
Where is the critical angle
Where total internal reflection takes place
120
What does the ciliary muscles do
Pull the lens for focusing
121
What does the cornea do
Lets light into the eye and begins focusing (refracting)
122
What does the iris do
Control the amount of light entering the eye
123
What does the lens do
Focus light onto the retina
124
What does the optic nerve do
Send signals to the brain
125
What does the pupil do
Let light through to the lens
126
What does the retina do
Light sensitive layer - sends signals to the optic nerve
127
What does the suspensory ligament do
Hold the lens in place
128
What are CCD's
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
How do CT scans work
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
How are X-rays used to treat cancer
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
What can you not do with a virtual image
Project it onto a screen
132
Examples of levers as force multipliers
Long sticks or bars
Wheelbarrows
Scissors
133
When is there a resultant moment
When the total anti-clockwise moments do not match the total clockwise moments
The object will then move
134
What is a magnetic field
A region where magnetic materials and wires carrying a current experience a force acting on them
135
Solenoid
Coil of wire
136
What is an electromagnet
A magnet whose magnetic field can be turned on and off with an electrical current
137
What is the function of a split-ring commutator
Swap the contacts every half turn to keep the motor rotating in the same direction
138
Electromagnetic induction
The creation of a potential difference across a conductor which is experiencing a change in magnetic field
139
Which coil has more turns in a step up transformer
Secondary
140
Which coil has more turns in a step down transformer
Primary
141
Where does current flow from
The positive to the negative
142
Where do electrons flow from
Negative to positive
143
In which materials do light travel fastest
Ones with lower refractive index
144
When is the only time total internal reflection can happen
When light is travelling from a more dense medium to a less dense one
