Physics Unit 3 Revision Flash Cards Produced by Mr P Scutt

Physics Unit 3 Revision Flash Cards

Produced by Mr P Scutt

What are the risks, and how can they be minimised, for an X-ray machine?

• 4 marks

Stimulating Challenging Innovative Exciting Nurturing Creative EngagingJohn O’Gaunt Science Team 2013 (Produced by Mr P Scutt)

What are the risks, and how can they be minimised, for an X-ray machine?

• X-rays ionises substances as it passes through.

• High doses can kill living cells• Low does can cause mutations and

cancerous growth

- Workers can wear badges that show how much radiation a person is exposed to.

How can distance measurements be made using a Ultrasound?

• 4 marks


How is the refractive index calculated?

• 3 marks


How can distance measurements be made using a Ultrasound?

• Use an oscilloscope to measure the ‘transit time’ of each pulse.

• This is the time taken from the transmitter to the boundary AND reflected back.

• Distance = speed x transit time • Depth therefore is 0.5 x speed x

transit time.

How is the refractive index calculated?

• n = sin i/sin r

• Where ‘i’ is the angle of incidence• ‘r’ is the angle of refraction

What is Snell’s Law?

• 3 marks


How does an endoscope work?

• 4 marks


What is Snell’s Law?

• Refractive Index = sin i/sin r

• Where ‘i’ is the angle of incidence• ‘r’ is the angle of refraction

• This is always the same value for a given material.

How does an endoscope work?

• This uses Total Internal Reflection• Where light is shone down a fine glass

wire (optic fibre)• At a critical angle (incident angle)• Where all of the light is reflected and no

refraction takes place (light does not escape the wire).

• This is used to view different parts of the body from the inside by passing the optic fibre down through the body.

Name the main parts of the eye

• 12 marks


How does the lens work in the eye?

• 3 marks


Name the main parts of the eye

Aqueous Humour

Vitreous Humour Eye Muscle

How does the lens work in the eye?

• The lens focuses the image on the retina

• It is thin for distant objects• It is thick for near objects

How can the lens of the eye be corrected for visual impairments?

• 4 marks


Draw a diagram to show a lever

• 3 marks


How can the lens of the eye be corrected for visual impairments?

• Short-sighted (cant see distant clearly) – so lens does not become thin enough – need a diverging lens.

• Long-sighted (cant see near objects) – so lens doesn’t become thick enough – need a converging lens.

Draw a diagram to show a lever

How can the centre of mass be worked out in a symmetrical object?

• 2 marks


How can the centre of mass be worked out in a irregular shaped object?

5 marks


How can the centre of mass be worked out in a symmetrical object?

• Draw the lines of symmetry on the object.

• Where the lines appear to cross if the point where the mass ‘appears’ to be concentrated.

How can the centre of mass be worked out in a irregular shaped object?

• Hang an object from a point• Hang a plumb line in front• Draw a line down the same line• Hang from a different point• Draw another line• Where the lines cross is the centre of

mass

How can the stability of an object be increased?

• 2 marks


Why does an object topple over?

• 2 marks


How can the stability of an object be increased?

• Lower the centre of mass (engine is low on a tractor)

• Increase the size of the base (e.g. a high chair with a wider base)

Why does an object topple over?

• An object topples over because its line of action (the line drawn straight down from the centre of mass)

• Falls outside the base of the object

How can pressure in liquids be used?

• 4 marks


What is a force multiplier?

• 5 marks


How can pressure in liquids be used?

• Liquids cant be compressed so can transfer a force from one area to another

• Used in car brakes and hydraulics

What is a force multiplier?

• As Pressure = Force/Area • And, liquids cant be compressed we

can use this in a hydraulic piston.

• Step one – work out the pressure on the liquid from one piston (pressure = force x area)

• The same pressure is transferred to the second piston.

• If you therefore know the pressure and area you can work out the force. If the area is bigger, the force is bigger (i.e. multiplied)

Example:Pressure = 10N/10cm = 1N/cm

Pressure = 1N/cm

1N/cm x 100cm = 100N

What is important about an object in circular motion?

• 4 marks


What affects the time period of a pendulum?

• 3 marks


What is important about an object in circular motion?

• Its velocity is constantly changing as it is always changing direction.

• So it is said to be in acceleration• Towards the centre of the circle• So this is called its centripetal

acceleration

What affects the time period of a pendulum?

• The amplitude of an oscillating object• The mass of the object• The length of the pendulum

Draw a labelled diagram of a pendulum

• 3 marks


How does an X-Ray machine work?

• 5 marks


Draw a labelled diagram of a pendulum

How does an X-Ray machine work?

• X-ray tube directed at patient • X-rays pass through body• Film on other side detects the x-rays• Absorbed by bones/teeth = appear white• Pass through soft tissue = appear black

• A contrast medium can be used to show up an organ (e.g. a barium meal to see parts of the digestive system)

• A CCD converts the X-rays to light so an image can be viewed on a computer

How does an CT Scanner work?

• 5 marks


What is an electromagnet and how can you affect its strength?

• 5 marks


How does an CT Scanner work?

• Creates a 3D image• X-ray rotates around the patient• Detector moves around on the opposite

side to the x-ray tube. • Detected by a computer which produces an

image. • Can distinguish between different soft

tissues. • Higher dose of X-rays than an ordinary x-

ray machine

What is an electromagnet and how can you affect its strength?

• A soft iron core with• Coils of wire wrapped around• It can be switched on and off

• Strength increased by• More coils of wire• More current

Where are electromagnets used?

• 3 marks


How does a loudspeaker work?

• 4 marks


Where are electromagnets used?

• Scrap yards

• Door Bell

• Relay switch

• Circuit breaker

How does a loudspeaker work?

• Due to the motor effect • Needs an alternating current (ac)• When current flows it forces the cone to

move. • When the current flows the other way

the force is reversed and so moves

• The frequency is determined by the frequency of the a.c. supply

How can you calculate a transformers efficiency?

• 4 marks


What is the transformers equation?

• 4 marks


How can you calculate a transformers efficiency?

• Primary potential difference x primary current

• Must equal (for 100% efficiency)

• Secondary potential difference x secondary current

What is the transformers equation?

pd across primary = number of turns on primary .pd across secondary number of turns on secondary

For a step up – number of turns is greater on secondary

For a step down – number of turns is greater on the primary

What is a moment?

• 3 marks


How does the length of spanner affect the size of the moment?

• 2 marks


What is a moment?

• A turning force• Calculated by force x perpendicular

distance • Measured in Nm

How does the length of spanner affect the size of the moment?

• Larger the distance, larger the turning effect (moment)

• Meaning it is easier to move an object.

Describe circular motion

• 7 marks


What does centripetal force depend upon?

• 6 marks


Describe circular motion

• Objects velocity is constantly changing• Because velocity is speed and direction• This means it is accelerating.• It must also have a force acting on it• Towards the centre of the circle• This is called the centripetal force• This force can be tension, friction or

gravity.

What does centripetal force depend upon?

• Mass• The heavier the object, the bigger the CF• Speed• The faster the object is moving, the

bigger the CF. • Radius• The smaller the radius, the larger the

force needed to keep it going in a circle.

How does gravity vary?

• 3 marks


What are the different types of satellites and how are they

different?• 12 marks


What is gravity and how is it used?

• Gravity is a force• The further the object is away, the

less the force of gravity acting on it. • Gravity is a centripetal force keeping

planets in orbit.

What are the different types of satellites and how are they

different?• Geostationary• Used for communication – tv, telephone• Have a high orbit• Over the equator • Appear to stay in the same position as the Earth rotates with them • 24 hour orbit time

• Low Polar Orbit• Used for weather and spying• Sweeps over both poles• Full orbit takes only a few hours• Allow whole surface to be observed• Clearer picture as lower than geostationary to observe weather etc.

What is the difference between a virtual and real image?

• 7 marks


When describing an image you need to describe?

• 3 marks


What is the difference between a virtual and real image?

• Real image is actually there• Formed when light from object comes together to

form image on screen • E.g. light falls on the retina in the eye

• Virtual image is not there• Formed when rays are diverging, so light from object

appears to be coming from a completely different place –

• E.g. mirror as face appears behind the mirror; • E.g. magnifying glass – bigger and further away than

image actually is

When describing an image you need to describe?

• How big it is – compared to original image.

• Whether it is upright or inverted (upside down)

• Whether it is real or virtual.

How are light rays reflected in a mirror. Draw a labelled diagram.

• 5 marks


What is refraction?

• 4 marks


How are light rays reflected in a mirror. Draw a labelled diagram.

• Angle of incidence = Angle of reflection

What is refraction?

• Where light bends• Caused by it changing speed• As ray passes through a different

medium (e.g. from air into water). • Light bends towards the normal

when moving to a denser medium (air into water)

Draw a diagram to show how an image is formed in a plane mirror.

• 5 marks


Draw a diagram to show how an image is formed in a concave

mirror. • 5 marks


Draw a diagram to show how an image is formed in a plane mirror.

Draw a diagram to show how an image is formed in a concave

mirror.

Draw a diagram to show how an image is formed in a convex

mirror. • 5 marks


Draw a diagram to show how an image is formed in a converging

lens. • 5 marks


Draw a diagram to show how an image is formed in a convex

mirror.

Draw a diagram to show how an image is formed in a converging

lens.

Draw a diagram to show how an image is formed in a diverging

lens. • 5 marks


What are the three rules for refraction in a converging lens?

• 3 marks


Draw a diagram to show how an image is formed in a diverging

lens.


• An incident ray parallel to the axis refracts through the lens and passes through the focal point on the other side.

• An incident ray passing through the focal point refracts through the lens and travels parallel to the axis.

• An incident ray passing through the centre of the lens carries on in the same direction.

What are the three rules for refraction in a diverging lens?

• 3 marks


Explain how a magnifying glass works.

• 3 marks



• An incident ray parallel to the axis refracts through the lens and travels in line with the focal point (so appears to have come from the focal point).

• An incident ray passing towards the focal point refracts through the lens and travels parallel to the axis.

• An incident ray passing through the centre of the lens carries on in the same direction.

Explain how a magnifying glass works.

• Use convex lens• Object is closer to lens than focal

length• Image is virtual (rays don’t actually

come from where they appear to be).

Explain how a camera works.

• 5 marks


What are the properties of sound?

• 5 marks


Explain how a camera works.

• Real image formed because light rays actually meet there

• Image is smaller than he object

• Object is further away than the focal length of the lens

• Inverted image (upside down)

What are the properties of sound?

• Travels as a wave• Can be reflected• Can be refracted• We can hear 20-20000Hz• Does not travel through vacuum

Draw a sound wave and explain how it changes with pitch and

volume. • 4 marks


What is Ultrasound and how does it work?

• 4 marks


Draw a sound wave and explain how it changes with pitch and

volume.

What is Ultrasound and how does it work?

• Has higher frequency than we can hear

• It can be partially reflected at a boundary between media

• Reflected signal can be detected • To produce an image

Where is ultrasound used and why?

• 9 marks


What is a solenoid?

• 4 marks


Where is ultrasound used and why?

• Cleaning• Clean very precise areas and • delicate objects• By causing vibrations• Clean teeth

• Quality control in metal castings• Can detect cracks inside material (weaknesses)

• Pre—natal scanning• Produce image of foetus from reflected waves

What is a solenoid?

• A coil of wire• With a magnetic field inside• Magnetic field on outside is like that

of a bar magnet• Has North and South pole

How do you work out the direction of a magnetic field through a wire?

• 3 marks


Which elements are magnetic?

• 3 marks


How do you work out the direction of a magnetic field through a wire?

Right-hand rule

Which elements are magnetic?

• Iron• Cobalt• Nickel• (Steel is an alloy made of iron and

carbon)

What is Fleming’s left hand rule?

• 3 marks


How can you speed up a simple electric motor?

• 4 marks


What is Fleming’s left hand rule?

How can you speed up a simple electric motor?

• More current• More turns on the coil• Stronger magnetic field• Soft iron core

What is meant by electromagnetic induction?

• 2 marks


How does electromagnetic induction work?

• 2 marks


What is meant by electromagnetic induction?

• The creation of voltage in a wire• Which is experiencing a change in

magnetic field.

How does electromagnetic induction work?

• Move a magnet in a coil or wire• Induces a voltage• Or vice versa (move coil in a

magnetic field)

What factors affect the size of the induced voltage in

electromagnetic induction?• 4 marks


What is the role and properties of a generator?

• 5 marks


What factors affect the size of the induced voltage in

electromagnetic induction?• Strength of the magnet• Area of the coil• Number of turns on the coil• The speed of movement

What is the role and properties of a generator?

• They rotate a coil • In a magnetic field• As the coil spins, a current is induced• The current changes direction every

half turn. • Have slip-rings and brushes

What is the role and properties of a dynamos?

• 3 marks


What is the role and properties of a transformers?

• 4 marks


What is the role and properties of a dynamos?

• They rotate the magnet instead of the coil

• Causes field through the coil to swop every half turn

• Used on bikes to power lights

What is the role and properties of a transformers?

• Change the voltage• Only works with alternating current• Step-up• Step-down

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Physics Unit 3 Revision Flash Cards Produced by Mr P Scutt