Ultrasound waves are partially ________ when they meet a boundary between two different media.
Refracted
Reflected
Ultrasound wave facts:
Can be produced by electronic systems
Have a frequency lower than 20000Hz
Have a frequency higher than 20000Hz
An electromagnetic wave beyond the red end of the visible spectrum
An electromagnetic wave beyond the blue end of the visible spectrum
X-rays have a very short wave length and cause ionisation
X-rays can't be used to diagnose and treat medical conditions
Properties of X-rays:
absorbed by metal and bone
transmitted by soft tissue
reflected by soft tissue
doesn't effect photographic film in the same way as light
effects photographic film in the same way as light
What is refraction?
change of direction of light as it passes from one medium to another
change of direction of sound waves as they pass from one medium to another
A lens forms an image by refracting light
how is the nature of an image defined:
Size relative to the object
If the light rays cross
Real or virtual
Upright or inverted
Distance from focal length
Which lens is used in a magnifying glass?
Converging
Diverging
Visible light can be sent along optical fibres
What is long sight caused by?
Eyeball being too short
Eyeball being to long
The lens is too weak
The lens is too strong
Where can the eye focus on objects?
Between the principal focus and the far point
Between the near point and the far point
Between the near point and the principal focus
The power of a lens is given by P=1/f
The greater the refractive index
The flatter the lens
The thicker the lens
What does a camera lens and the eye have in common?
The CCDs in a digital camera is the equivalent of the retina
They are both diverging lens'
They are both converging lens'
Focal length is determined by:
Refractive index of the material
Thickness of the lens
Curvature of the lens
Light rays
Power is measured in Dioptres, D
The time period depends on the force being applied
The centre of mass of a symmetrical object is:
In the middle
Along its axis of symmetry
The centre of mass is that point where the mass of an object is thought to be
Centered
Concentrated
Clear
What is the turning effect of a force called?
Moment
Resultant
If the line of action of weight of an object lies inside the base of the object there will be a resultant moment and it will topple.
What is the moment of a force measured in?
D (dioptres)
m/s (metres per second)
Nm (Newton-metres)
the centripetal force need to make an object perform circular motion increases as:
Mass decreases
Mass increases
Radius decreases
Radius increases
Speed decreases
Speed increases
The acceleration towards the centre of a circle changes the direction of the body and its speed.
What is the resultant force causing acceleration called?
Centripecal force
Centripical force
Centripetal force
Liquids are compressible
Pressure in liquids is transmitted equally in all directions
Using different cross sectional areas of a hydraulic system means it can be used as a force multiplier.
what is produced around a wire when current flows though it?
Heat
Magnetic field
The size of a force can be increased by:
Increasing the size of the wire
Increasing the size of the current
Increasing the size of the voltage
Increasing the strength of the magnetic field
When will the conductor not experience a force?
When parallel to the magnetic field
When bearer to the magnetic field
In flemings left hand rule:
the first finger is the magnetic field direction
The second finger is the strength of the current
The second finger is the direction of the current
The thumb is the direction of the current
The thumb is the motion of the wire
Switch mode transformers use a lot of power when are switched on but no load is applied.
Switch mode transformers are much lighter and smaller than normal transformers working from a 50Hz mains supply
What does it mean if the electrical power input is equal to the electrical power output in a transformer?
It is 100% efficient
Heat energy was lost
Its 0% efficient
In a step down transformer:
The potential difference across the secondary coil is more than the potential difference across the primary coil
The potential difference across the secondary coil is less than the potential difference across the primary coil
In a step up transformer:
What does an alternating current in the primary coil produce?
A changing magnetic field
A constant current
What does a changing magnetic field induce in a transformer?
An alternating potential difference across the secondary coil
An constant potential difference across the secondary coil
If a magnet is moved into a coil or wire of potential difference is induced across the ends of the coil
If an electrical conductor cuts through a magnetic field a potential difference is induced across the ends of the conductor
Which of these options are part of the basic structure of a transformer?
Two coils around a soft core
One coil around a soft core
De magnetising soft iron
Magnetising soft iron
Layers of iron (Laminated)
One layer (meaning laminated)
