P13 - Electromagnetic Spectrum Flashcards
What are electromagnetic waves?
Electromagnetic waves are a group of transverse waves. They are sometimes called electromagnetic radiation. They consist of vibrating electric and magnetic fields, which is why they can travel through a vacuum - don’t rely on vibrating matter.
What is the spectrum?
The spectrum means there are different parts/types or electromagnetic waves. All waves in this spectrum have the same speed/velocity.
Smallest wavelengths to longest wavelengths on the spectrum
Gamma X-ray Ultraviolet Visible Light
Infra red Microwaves Radio waves
Shortest wavelength to longest wavelength of visible colour
Violet Indigo Blue Green Yellow Orange Red (red is the last colour you can see before it is infra red)
What is infrared radiation?
Infrared radiation is absorbed by your skin. It can damage, burn or kill skin cells because it heats up the cells.
What can infrared radiation be used for?
Keeping premature babies warm
Used on farms for chicks
Infrared Devices
Optical fibres used in communications systems and medical procedures usually use infrared radiation instead of visible light. This is because infrared radiation is absorbed less than visible light in glass fibres. IR has a wide range of different wavelengths.
What are optical fibres?
A glass or plastic pipe through which IR wavelengths are transmitted.
Properties of microwaves
Longer wavelength than infrared
More dangerous than IR
Less warm than infrared
Water molecules in food absorb microwave - more kinetic energy, more thermal energy
More hydrated food - more effective heating
Shorter wavelength than radio waves
Microwaves can penetrate the atmosphere, therefore used for satellite TV
Also carry mobile phone signals
Microwave ovens heat food faster than normal ovens because microwaves can penetrate into food and are absorbed by water. Normal ovens don’t absorb microwaves.
Properties of radio waves
Range from 300,000 Hz to 3000 million Hz
Radio waves are used to carry radio, TV and mobile phone signals
You can use radio waves to connect a computer to other devices such as a printer/computer mouse
Radio waves can be hazardous - penetrate peoples bodies and heat internal parts
Phones transmit/receive radio waves
E.g. Bluetooth (a radio wave) enabled devices can communicate over 10 metres without the need for cables (waves sent out and received)
Transmitting radio waves - Steps in diagram
- Oscillator supplies carrier waves to the transmitter in an alternating current (repeatedly reversing direction when electrons move back and forward).
- Audio signal is interpreted by the transmitter and modulates carrier waves .
- Modulated carrier waves from the transmitter are supplied to the Ariel. This emits radio waves carrying audio signal due to alternating current.
- Radio waves are absorbed by a receiver Ariel inducing alternating current in the receiver Ariel and causing oscilllations.
- The frequency of the oscillations in the receiver is the same as the frequency of the radio waves.
- Receiver circuit separates audio signal from the carrier waves. Audio signal is supplied to a loudspeaker which send out sound waves similar to the sound waves received by the microphone in the radio station.
Absorption and emission of infrared radiation
Black absorbs more heat than white
White reflects light
Black is a good absorber and a good emmitter of heat
Ultraviolet light properties
Used for security marking - bank notes and property, etc
Can also be used for sterilisation
Can go through clouds - causes skin cancer
Radio stations
FM only has a 30 mile range
AM - 150 mile range - long wave, further distance but signal quality is worse when long wave frequency
What are x-rays?
When electrons are released by electrical supply, which hits an object and produces X-rays.
Can’t go through metal (bone)
Can pass through soft tissues
More high energy/powerful than UV
Radio therapy - X-rays can treat cancer
Can’t have X-rays when pregnant
If doctors are exposed to X-rays, a safety badge tells you how much ionising radiation you have received (if you have been exposed) if so, can’t use X-rays as it could be dangerous
Can also be used for checking materials (find cracks where X-rays leak through)
How are X-rays produced?
When electrons or other particles moving at high speed are stopped - X-ray tubes used to produce X-rays
What is gamma radiation?
When radioactive element decay, gamma rays are emitted in electromagnetic waves. Very dangerous.
How are x-rays used in hospitals?
• to make images of your internal body parts
• to destroy tumours at or near the body’s surface
What are x-rays usually absorbed by?
• bones and teeth as opposed to soft tissues
What does radiation dose depend on?
• the type of radiation used
• how long the body is exposed to it
• the energy per second absorbed by the body from radiation
What is a contrast medium?
a substance that can fill an organ containing soft tissue that absorbs X-rays easily
• enables the internal surfaces in the organ to be seen on the radiograph
e.g. to obtain a radiograph of the stomach a patient is given a barium meal before hand because barium is a good absorber of X-rays
What stops x-rays reaching other parts of the body?
• lead plates between the tube and the patient
• X-rays reaching the pass through a gap between the plates
• lead is used because it is a good absorber of X-rays
X-ray therapy
• carry much more energy than x-rays used for imaging
• used to destroy cancerous tumours in the body
• shorter in wavelength than X-rays for imaging
Why are low-energy x-rays useful for imaging?
Low-energy X-rays are suitable for imaging because they
are absorbed by bones and teeth but they pass through soft tissue and gaps such as cracks in bones. Low-energy X-rays do not carry enough energy to destroy cancerous tumours.
In the motor effect, how can the size of the force be increased?
• increasing the current
• using a stronger magnet
The size of the force depends on the angle between the wire and the magnetic field lines. The force is:
• greatest when the wire is perpendicular to the magnetic field
• zero when the wire is parallel to the magnetic field lines.
Direction of force in the motor effect
right angles to the wire and the field lines. Also, the direction of the force is reversed if either the direction of the current or the magnetic field is reversed.
Fleming’s left hand rule
Thumb = movement
First finger = magnetic field direction
Second finger = current
How to measure the frequency of waves using a ripple tank
Set up the ripple tank as shown in the diagram with about 5 cm depth of water.
Adjust the height of the wooden rod so that it just touches the surface of the water.
Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.
Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take measurements from the still picture.
Count the number of waves passing a point in ten seconds then divide by ten to record frequency.
Calculate the speed of the waves using: wave speed = frequency × wavelength.
Measuring waves in a solid practical
Attach a string or cord to a vibration generator and use a 200 gram (g) hanging mass and pulley to pull the string taut as shown in the diagram. Place a wooden bridge under the string near the pulley.
Switch on the vibration generator and adjust the wooden bridge until stationary waves can be clearly observed.
Measure the length of as many half wavelengths (loops) as possible, divide by the number of half wavelengths (loops). This is half the wavelength, doubling this gives the wavelength.
The frequency is the frequency of the power supply.
Calculate the speed of the waves using: wave speed = frequency × wavelength.
