Physics Unit 3

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  • Created by: jenni2906
  • Created on: 14-05-15 18:55
What is the shape of the lens changed by?
Ciliary muscles.
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What focuses light onto the retina?
The cornea and the lens.
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What are two similarities between an eye and a camera?
Both use a converging lens and image formed is real.
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How does a starter motor operate?
Current flows through the coil and magnetic field is produced. Short side of iron bar attracted to electromagnet. Contacts pushed together by iron bar. Starter motor circuit is completed. Current flows through started motor.
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Why does the radiographer go behind a screen during an X-ray?
X-rays are ionising. Any stray X-rays are absorbed by the screen which reduces the radiation dose to the radiographer.
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What is the advantage of a CT scan compared to an X-ray?
A CT scan gives a 3D so the image can be observed from different directions.
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How do you work out the refractive index?
sin i divided by sin r.
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What is meant by the term centre of mass?
Where the mass of the object can be thought to be concentrated.
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How can you change an object to increase stability?
Lower the centre of mass and make the base wider.
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Why does the object not topple over?
The line of action of its weight falls inside its wheel base so there is no resultant moment.
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How does a transformer work?
An alternating input is supplied to the primary coil which produces an alternating magnetic field in the iron core. This magnetic field links with the secondary coil which increases an alternating voltage across the secondary coil.
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What is ultrasound?
Soundwaves which have a frequency higher than the upper limit of hearing for humans.
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What are the uses of ultrasound scanning?
Pre-natal scanning, removal of kidney stones, ******** scanning.
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Disadvantage of CT scanning.
The X-ray used are ionising.
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How is a transformer constructed?
A laminated core is made from iron. There are 2 coils made of copper and covered in insulation.
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Step up transformer?
More turns on the secondary coil than the primary. Output potential difference is greater than the input.
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Step down transformer?
Less turns on the secondary coil than its primary. Output potential difference is lower than input potential difference.
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What type of transformer is used in a mobile phone charger?
Switch-mode transformer.
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Name two causes of long sight.
The eye is too short. The lens cannot focus an image at the retina.
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Where is light refracted to produce an image?
Cornea, retina, lens.
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Where are images focused?
Retina, charged coupled device.
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What is the variable where light enters?
Pupil, aperture.
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What is one advantage of making spectacles using lenses made from glass of a higher refractive index?
Lenses can be made thinner.
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How do you find the centre of mass of an object?
Suspend shape from a point, attach pendulum to point. Draw vertical line on card where string rests. Suspend card from new point and draw line where string rests. Where the points cross is the centre of mass.
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Why may an object tip?
The weight lies outside the base so there will be a resultant moment.
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Why does the ray of light stay within the optical fibre?
The angle of incidence is greater than critical angle.
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What type of system uses a liquid to transmit a force?
A hydraulics system.
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Why does a loudspeaker cone vibrate when an AC current flows through the coil?
Current flowing through the coil creates a magnetic field around the coil which interacts with the permanent magnetic field. This produces a resultant force when the direction of the current changes, the direction of the force changes to the opposite
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What is an X-ray image?
High frequency, short wavelength electromagnetic wave. They are transmitted through healthy tissue and absorbed by bones. Can diagnose bone fractures or dental problems. Formed using a CCD.
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How can X-rays treat cancer?
The X-rays are focused on the tumour using a wide beam, this beam is rotated round the patient with the tumour at the centre, 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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How does ultrasound imaging work?
When the wave passes from one medium to another, some of the wave is reflected off the boundary between the two medias. This is partial reflection. Some of the ultrasound gets reflected back to the detector.
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Compare the safeness of ultrasound, CT scans and X-rays.
Ultrasound waves are non-ionising. X-rays are ionising. CT scans use more X-ray radiation than standard X-rays.
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Compare the image quality of ultrasound, CT scans and X-rays.
Ultrasound images are fuzzy. X-rays produce clear iamges of the bones and metal. CT scans produce detailed images that can be used to diagnose complicated illnesses.
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What is a convex lens?
A converging lens - it bulges outwards.
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What is a concave lens?
A diverging lens - it caves inwards.
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How do you draw a ray diagram for a converging lens?
Draw a ray from the top of the object parallel to the principal axis, draw a ray going through the middle of the lens, draw a ray from the parallel line through the principal axis, where the points meet is the top of the image.
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Describe the image of the converging lens.
Inverted. Real. Smaller than the object.
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How do you draw a ray diagram for a diverging lens?
Same as the converging lens but last ray goes through the principal focus on the left rather than the right.
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Describe the image of the diverging lens.
Upright. Virtual. Smaller than the object.
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What is the formula for magnification?
Image height divided by object height.
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How do you work out the power of the lens?
Power (D) = 1 divided by focal length (m).
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What is the near point and the average near point?
The closest distance the eye can focus on. 25cm.
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What is the far point?
The furthest distance that the eye can focus comfortably. Infinity.
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What is short sight and how is it corrected?
People that can't focus on distant objects. Caused by the eye being too long and can't focus an image on the retina. Corrected by diverging lens - diverges the light before it enters the eye.
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What is long sight and how is it corrected?
People that can't focus clearly on near objects. Eyeball is too short and the eye can't focus an image on the retina. Corrected by converging lens - light refracts and converges before it enters the eye so image can be focused on the retina.
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How do lasers surgically correct eye problems?
Cauterise small blood vessels as they cut through the tissue. Laser vapourises the cornea to change its shape which changes the focusing ability.
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How do you work out the refractive index and critical angle?
Refractive index = 1 divided by sin c.
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What is a moment?
The turning effect of a force.
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How do you work out a moment?
Moment = force x distance.
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What is the centre of mass?
The point at which the whole mass is concentrated.
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How do objects turn?
If the total anticlockwise moments do not equal the total clockwise moments, there will be a resultant moment.
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How do you work out the time period?
Time period = 1 divided by frequency.
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How do you work out the pressure?
Pressure (Pa) = force divided by cross-sectional area (m squared).
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What is the force that keeps something moving in a circle called?
The centripetal force.
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What is a magnetic field?
A region where magnetic materials and also wires carrying currents experience a force acting on them.
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What do the fingers stand for in flemings left hand rule?
Thumb = motion. First finger = field. Second finger = current.
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What two factors speed up a motor?
Current and stronger magnetic field.
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What is the transformer equation?
potential difference across primary divided by potential difference across secondary = number of turns on primary divided by number of turns on secondary.
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What is a switchmode transformer?
A type of transformer that operates at higher frequencies than traditional transformers.
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Other cards in this set

Card 2

Front

What focuses light onto the retina?

Back

The cornea and the lens.

Card 3

Front

What are two similarities between an eye and a camera?

Back

Preview of the front of card 3

Card 4

Front

How does a starter motor operate?

Back

Preview of the front of card 4

Card 5

Front

Why does the radiographer go behind a screen during an X-ray?

Back

Preview of the front of card 5
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