P12 Flashcards
What type of lens is thicker in the middle than at the edges?
Convex lenses
Which type of lens causes light rays to diverge?
Concave
Which type of lens is used in a camera?
convex
What is a real image?
A real image is an image that can be projected onto a screen
What is a virtual image?
An image from which rays of light appear to come but do not do so in reality
What types of images do concave lenses form?
Only virtual images
What name is given to a material that absorbs some wavelengths of visible light and transmits others?
A filter
Why can we see through glass?
Almost all light waves are transmitted through glass, making it a transparent object
What name is given to the distance between the lens and the principal focus?
Focal length
What is an area of low pressure in a wave called?
A rarefraction
What is denser (air, glass or water)?
Glass
What happens to a light ray when it travels from water into air?
It bends away from the normal because it passes into a less dense material and speeds up
What are the units for magnification?
Magnification has no units since it is a ratio of 2 quantities with the same units.
What state of matter does sound travel the fastest?
Solids, because the particles are more tightly packed
Waves transfer ____
energy from place to place, without transferring any matter
What is the amplitude?
The amplitude of a wave is the distance from the centre line (or the still position) to the top of a crest. or to the bottom of a trough.
What is frequency?
Frequency is the number of complete waves passing a certain point per second measured in Hz. 1 Hz is equal to 1 wave per second.
What is wavelength?
The wavelength of a wave is the distance between a point on one wave and the same point on the next wave.
What are transverse waves?
Transverse waves are waves whose oscillations are at right angles to the direction of travel and energy transfer.
What are longitudinal waves?
In longitudinal waves, the oscillations are along the same direction as the direction of travel and energy transfer. (parallel)
Examples of transverse waves
All EM waves and ripples on water
Examples of longitudinal waves
Sound waves, seismic waves, P- waves
What is the frequency range of human hearing?
20Hz - 20KHz
What is reflection?
Reflection involves a change in direction of waves when they bounce off a barrier.
What is refraction?
Refraction is the process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium.
What is the angle of incidence?
The angle of incidence is the angle between the incoming wave and the normal.
What is the angle of reflection?
The angle of reflection is the angle between the reflected wave and the normal.
Angle of Incidence is greater/equal/less than the Angle of Reflection
Angle of Incidence = Angle of Reflection
What is the law of reflection?
The law of reflection states that, on reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray.
What is specular reflection?
Specular reflection happens when a wave is reflected in a single direction by a smooth surface E.g when light is reflected by a mirror you get a nice clear reflection
What is diffuse reflection?
Reflection from a rough surface is called diffuse reflection because the reflected rays are scattered in lots of different directions
high to low Electromagnetic Spectrum?
radio - microwave - infared - visible light - ultraviolet - x-rays - gamma rays
what is radio waves used?
used to broadcast radio and television
what is microwaves used for?
cooking,radar,telephone and other signals
what is infared used for?
transmits heat from sun, fires radiators
what is visible light used for?
makes things to be seen
what is uv used for?
absorbed by skin
what is rays used for?
used to view inside bodies and objects
what is gamma rays used for?
used in medicine for killing cancer cells
3 things all electromagnetic waves have in common
- transfers radiation as energy from waves
- can travel through a vacum
- travel at same speed
What is the speed of light in a vacuum or air?
300,000,000 m/s
Which colour is the best absorber of radiation?
Black
What gases in the atmosphere change the balance of infrared radiation absorbed and emitted by the Earth?
Greenhouse gases change the balance of infrared radiation absorbed and emitted by the Earth.
What health effects can ultraviolet waves cause?
Cause the skin to age prematurely and increase risk of developing skin cancer
Uses of radio waves
Radio waves are used for communication such as broadcasting television and radio, communications and satellite transmissions.
What is echo?
A reflection of sound waves from a smooth surface
Uses of infrared
- security systems
- thermal imaging
- electrical heaters
Define ultrasound
Ultrasound is sound with a frequency greater than 20,000 Hz
