AQA GCSE Physics EM waves

Define electromagnetic waves and state what they do

Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber. Examples of evidence that EM waves transfer energy

Name the seven types of electromagnetic wave, in the correct order from longest to shortest wavelength

Electromagnetic waves form a continuous spectrum and the waves that form the electromagnetic spectrum are grouped in terms of their wavelength and their frequency. Going from long to short wavelength (or from low to high frequency) the groups are: radio, microwave, infra-red, visible light (red to violet), ultra- violet, X-rays and gamma-rays

Statue the range of wavelengths in the EM spectrum

The range of wavelengths is approximately 10^-15m - 10⁴m

Describe the properties common to all EM waves 

All EM waves are transverse

All types of EM waves travel at the same velocity through a vacuum or air

State the significance of visible light

Our eyes detect visible light and so only detect a limited range of electromagnetic waves

Briefly describe how EM waves are produced

Changes in the atom and their nuclei leads to atoms generating and absorbing frequencies of EM radiation over a wide frequency range. Orbital electrons need to absorb EM radiation of a particular frequency to move up into a given higher energy level. Electrons emit EM radiation of a particular frequency when they move down into a given lower energy level. Changes in nuclei produce gamma radiation

Describe how EM waves can be different to each other in terms of their interactions with different substances

Different wavelengths of electromagnetic waves are reflected, refracted, absorbed or transmitted differently by different substances and types of surface

Describe how radio waves can be produced in electrical circuits

Radio waves can be produced by oscillations in electrical circuits

Describe the effect of radio waves on electrical circuits

When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can also produce oscillations in an electrical circuit

State some practical applications of radio waves

Radio waves are used for TV and radio

Explain why the properties of microwaves make them suitable for their applications

Microwaves are transmitted by the Earth's atmosphere. Some microwaves are easily absorbed by water molecules

State main uses of ultraviolet and explain how the properties of ultraviolet make them suitable for their use

UV is used in sun-tan beds, and energy efficient lamps - They can cause objects to flouresce and can cause skin to darken

State medical and non-medical uses of X-rays and explain how the properties of X-rays make them suitable for their use

X-rays and gamma rays can be used for medical imaging and treatments. Gamma rays can also be used as tracers and to sterilise surgical instruments

Describe how gamma rays are produced

Gamma rays originate from changes in the nucleus of an atom

State medical and non-medical uses of gamma rays and explain how the properties of gamma rays make them suitable for their use

1. Sterilising medical instruments, even in their packages - makes it safer. They are highly penetrating

2. Medical tracers are used to follow the flow of substance throughout the body. Highly penetrating, allowing them to pass through the body. Weakly ionising so it minimises the risk of cell damage compared to alpha or beta

3. Treating cancer. Highly penetrating so it can be focused on the tumour to kill it. Weakly ionising so minimises damage to healthy cells

State the parts of the EM spectrum that are ionising and describe the types of harm that ionising radiation could cause to the human body tissue

UV can cause skin to age prematurely. Can increase the risk of skin cancer. X- rays and gamma rays can cause mutations and can cause cancer

Define radiation dose and state factors that affect the level of harm that ionising radiation can do the body

Radiation dose (in sieverts) is a measure of the risk of harm resulting from an exposure of the body to the radiation. 1000 millisieverts (mSv) = 1 sievert (Sv)

Describe the difference between specular reflection and diffuse reflection

Reflection from a smooth surface in a single direction is called specular reflection. Reflection from a rough surface causes scattering: this is called diffuse reflection

Describe the difference between a transparent object and a translucent object

Objects that transmit light are either translucent or transparaent

Define the terms opaque, and explain why we see certain opaque objects as white and why we see certain opaque objects as black

If all wavelengths are reflected equally the object appears white. If all wavelengths are absorbed the objects appears black

Explain why we see opaque objects as a particular colours

The colour of an opaque object is dependent on the differential absorption, transmission and reflection of different wavelengths of light by the object. It is determined by which wavelengths of light are more strongly reflected. Wavelengths that are not reflected are absorbed or transmitted

Explain how colour filters work and what the colours of opaque objects would be when seen through particular coloured filters

Colour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour)

State what a lens does to light

A lens forms an image by refracting light

Describe the difference between what a convex lens and what a concave lens does to light

In a convex lens, parallel rays of light are brought to a focus at the principal focus. In a concave lens, parallel rays diverge as if they have come from a principal focus

Defne the terms principal axis, principal focus, and focal length, and draw them on a diagram

Principal axis - an imaginary straight line which passes through the optical centre of a lens and is perpendicular to its surface

Principal focus - Where all the rays meet on the principal axis

Focal length - the distance from the lens to the principal focus

Use the magnification equation to calculate magnification, image size or object size

Magnification = image size/actual size

Image height and object height should both be measured in either mm or cm. Magnification is a ratio and so has no units

Upright vs inverted images

Upright - right way up

Inverted - upside down compared to the object

Magnified vs diminished

Magnified - larger than object

Diminished - smaller than object

Real vs virtual images

Real - an image that can be projected onto a screen

Virtual - appears to come from behind the lens

Describe the images formed by a convex lens when the object is at different distances from the lens using the key terms

The image produced by a convex lens can be either real or virtual

Describe the image formed by a concave lens with the object at any distance from the lens using the key terms

The image produced by a concave lens is always virtual

State main uses of visible light and explain how the properties of visible light make them suitable for their use

Visible light is used in fibre optic cables - it is easily reflected and it passes down a fibre without being absorbed of scattered much. Also used in telescopes, microscopes, glasses, cameras

State which types of objects emit and absorb IR radiation

All bodies (objects), no matter what temperature, emit and absorb infrared radiation

Describe how the relationship between the amount of IR radiation emitted by an object and the amount of IR absorbed by that object affects the temperature of the object

The hotter the body, the more infrared radiation it radiates in a given time

State main uses of infrared radiation and explain how the properties of infrared radiation make them suitable for their use

Infrared is used in cooking and electric heaters and in thermal energy cameras - absorbing IR causes an object's temperature to increase

RP 10 - Investigate how the amount of IR radiation emitted / absorbed from an object depends on the surface texture/colour of that object

Rough (matte) and black surfaces are the best absorbers and emitters of IR. Shiny white surfaces are the best reflectors and worst absorbers and emitters of IR radiation

Define a black body

A perfect black body is an object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation.

Describe the relationship between the temperature of an object and the intensity of the wavelengths emitted by that object

All bodies (objects) emit EM radiation. The intensity and wavelength distribution of any emission depends on the temperature of the body

State the condition necessary for an object to remain at a constant temperature in terms of the emission and absorption of all EM radiation

A body at constant temperature is absorbing radiation at the same rate as it is emitting radiation

Explain how the temperature of the Earth's surface and atmosphere changes over a 24 hr period due to the changes in how much EM radiation is emitted, absorbed, and reflected by the Earth's surface and atmosphere, using everyday examples

The temperature of the Earth depends on many factors

including: the comparative rates of absorption of radiation, emission of radiation, and reflection of radiation into space