# Physics Unit 3 Revision

What are the properties of X ray waves?
High frequency, short wavelength + electromagnetic waves
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What are Xrays absorbed or transmitted by?
Transmitted (pass through) healthy tissue. Absorbed by denser materials like bones and metal
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Define ionisation
ionising radiations which can damage living cells. This happens because ionising radiation can break molecules into bits called ions. These ions can then take part in other chemical reactions in the living cells. This can cause cancerous cells
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How do Xrays treat cancer?
1)Xrays are focused on the tumour using a wide beam. 2)This beam is rotated round the patient with the tumour at the centre 3)This minimises the exposure of normal cells to radiation, and so reduces the chances of damaging the rest of the body
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-Wear lead aprons -stand behind a lead screen -Leave the room whilst scanning
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What is the frequency of ultrasound?
Higher than human hearing - 20,000Hz
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What is the range of human hearing?
20 Hz to 20 000 Hz
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What happens to ultrasound waves when they meet a boundary between 2 different media
Ultrasound waves are partially reflected when they meet a boundary between 2 different media. The time taken for the reflections to reach a detector can be used to determine how far the boundary is
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How can ultrasound be used in medicine?
Pre-natal scanning and removal of kidney stones
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s = v x t
s = distance in m / v = speed in m/s / t = time in seconds
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How do ultra sounds break down kidney stones?
Turns the kidney stones into sand like particles. These then pass through the urine
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What is refraction?
Is the change of direction of light as it passes from one medium to another
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How does a lens form an image?
By refracting light
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What is the distance from the lens to the principle focus called?
Focal Length
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Refractive Index =
Sin i / Sin r (i = angle of incidence r=angle of refraction)
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How can an image be described?
Real/Virtual - Upright/Inverted - Magnified/Diminished
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Describe a converging lense
Convex. It bulges outwards causing parallel rays of light to converge at the principle focus
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Descibe a diverging lense
Concave. It caves inwards and causes parallel rays of light to diverge (spread out)
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An incidence ray passing through the centre of the lens carries on in the same direction. What are the other rules for refraction in Converging Lenses?
1)A ray parallel to the axis refracts through the lens and passes throught the principle focus on the other side 2)A ray passing through the principle focus refracts through the lens+ travels parallel to the axis
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An incidence ray passing through the centre of the lens carries on in the same direction. What are the other rules for refraction in a Diverging lens?
1)A ray parallel to the axis refracts through the lens and travels in line with the principle focus on the other side 2)A ray passing through the lens towards the principle focus refracts through the lens and travels parallel to the axis
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Magnification =
Image Height / Object Height
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Power (D) =
1 / Focal Length (m)
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Draw the structure of an eye
.
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What is the function of the pupil/iris?
The iris is the coloured part of the eye and is made of muscle which controls the light intensity entering the eye. The pupil is the hole in the middle of the iris
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What is the function of the retina?
This is where images are formed and is covered in the light-sensitive cells. These detect light and send signals to the brain to be interpreted
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What is the function of the lens/
Changes shape to focus light from objects at various distences.
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What is the function of the cornea?
The cornea is a transparent 'window' with a convex shape and a high refractive index.
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What is the function of the ciliary muscle?
It connects to the lens by the suspensory ligaments and when the ciliary muscles contract, tension is released and the lens takes on a fat and more spherical shape.
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What is the function of the suspensory ligaments?
Slacken or stretch as the ciliary muscles contract or relax, to adjust the thickness and curvature of the lens.
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How do you correct vision?
By using convex and concave lenses
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What causes long sight?
The eyeball being too short or the eye lens being unabke to focus
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What causes short sight?
The eye ball being long or the eye lens being unable to focus
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What is the near point and the far point?
Near point is approx 25cm and the far point is infinity
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Draw the structure of a camera.
.
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What are the similarities in the structure of the camera with the structure of the eye?
The film in the camera is the equivalent to the retina in the eye. The image formed is real and inverted.
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The equation for power of a lens?
P = 1 / f (Power in dioptres and focal length in metres)
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What is the focal length of a lens determined by?
The refractive index of the material from which the lens is made and The curvature of the 2 surfaces of the lens
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Refractive index =
1 / Sin c
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What can visible light be sent along?
Optical fibres
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Define centre of mass
The point at which the mass of an object is thought to be concentrated
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Where is the centre of mass of a symmetrical object?
Along the axis of symmetry
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What does the time period of a pendulum depend on?
The length of the pendulum
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What is a moment?
The turning effect of a force
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What is the equation for the size of the moment?
M = F x d (Moment in newton-metres, d = the perpendicular distance from the line of action of the force to the pivot in metres)
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What is the moment of an object which is not moving?
The total clockwise moment must be exactly balanced by the total anticlockwise moment about any pivot
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When will something topple?
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
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Are liquids virtually incompressible?
Yes and the pressure in a liquid is transmitted equally in all directions
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The force exerted at one point on a liquid will be transmitted to other points in the liquid. What does this mean?
They have the multiplier effect
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What is happening when an object is moving continuously in a circle?
It continuously accelerates towards the centre of the circle
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What is the resultant force causing the acceleration in a cirle?
Centripetal force and it's always in the direction towards the centre of the circle
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The centripetal force increases when?
The mass of the object increases, The speed of the object increases. The radius of the circle decreases
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When a current flows through a wire, What is produced?
A magnetic field is produced around the wire
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How can the size of the force be increased in the motor effect?
Increasing the strength of the magnetic field and increasing the size of the current
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When will the conductor not experience a force?
If it is parallel to the magnetic field
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What hand is used in Fleming's rule (motor effect)?
Left hand
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What do the 3 fingers represent in Fleming's left hand rule?
1st = field, 2nd = current, thumb = motion
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I an electrical conductor 'cuts' through a magnetic field, what is induced?
A potential difference across the ends of the conductor
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Draw a basic transformer
.
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An alternating current in the primary coil produces what in the iron core and hense in the secondary coil? And what does this do?
A changing magnetic field. This then induces an alternating potential difference across the ends of the secondary coil
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What is the equation relating the potential difference across the primary and secondary coils
Vp / Vs = Np / Ns
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What is the equation relating the electrical power output would equal the electrical power input?
Vp / Ip = Vs / Is
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What is the frequency switch mode transformers work at?
50kHz and 200kHz
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## Other cards in this set

### Card 2

#### Front

What are Xrays absorbed or transmitted by?

#### Back

Transmitted (pass through) healthy tissue. Absorbed by denser materials like bones and metal

### Card 3

#### Front

Define ionisation

### Card 4

#### Front

How do Xrays treat cancer?