Chapter 6: Waves Flashcards
What is an electromagnetic wave?
Oscillating electric and magnetic fields that move at the speed of light
What do all waves do?
Transfer energy
What are transverse waves?
Waves where the oscillations are perpendicular to the direction of energy transfer (e.g. electromagnetic waves, water waves). Not all transverse waves require a medium
What equation links period (time taken for a wave to be produced) to wavelength?
P = 1/f P = period (s) f = Frequency (Hz)
What equation links wave speed to frequency and wavelength?
V = fλ V = Speed (m/s) f = Frequency (Hz) λ = Wavelength (m)
What are longitudinal waves?
Waves where the oscillations are parallel to the direction of energy transfer (e.g. sound waves). These waves all require a medium such as air
What is special about transverse waves?
It’s the wave that moves and not the medium
How would you measure the speed of sound?
- Get a stopwatch
- Stand 500 metres away from someone with 2 cymbals
- Start timing when you see the person smash the cymbals together
- Stop timing when you hear the sound
- Calculate a mean and use s=d/t to calculate the speed of sound
What is a wave’s frequency?
Number of waves passing a point per second
How are electromagnetic waves produced?
When atoms are heated, electrons move from outer shells to inner shells (higher energy levels). When electrons return to their original shells, electromagnetic waves (e.g. light) are produced. Alternatively, unstable nuclei can release energy in the form of electromagnetic waves (gamma waves)
What are some of the dangers of electromagnetic waves?
When absorbed, high frequency electromagnetic waves can knock electrons off atoms, causing chemical changes which can lead to DNA mutations and cancer
How are radio waves transmitted and received?
Radio waves are produced when electrons oscillate in AC electrical circuits. The opposite process takes place in receivers
What is the electromagnetic spectrum?
From low to high wavelength: Radio waves, Microwaves, Infrared, Visible, Ultraviolet, X-ray, Gamma ray
What are the uses of radio waves?
Transmitting radio and terrestrial TV signals (they can spread out easily and travel long distances before being absorbed). We can also send radio waves very long distances around earth, due to the fact that they reflect off the ionosphere
What are the uses of microwaves?
Heating up food (water molecules in the food absorb the energy of the waves and heat up, causing the temperature of the food to increase). They are also used to communicate with satellites in space (they can pass through the atmosphere without being reflected or refracted)
What are the uses of infrared?
Emitted by electrical heaters, used to cook food in ovens (infrared radiation energy is easily absorbed by the surface of objects). Infrared is also used in infrared cameras to detect heat losses from buildings
What are the uses of visible light?
Fibre-optics (used to transmit pulses of light down cables). Due to the short wavelength of visible light it can transmit a high amount of information
What are the uses of ultraviolet?
Energy-efficient light bulbs (UV is higher energy than visible). The energy of the UV is captured by the internal surface of the bulb and converted into visible light. This requires less energy than a normal light bulb. UV is also used for tanning (can increase cancer risk)
What are X-rays and gamma rays used for?
X-rays are used to scan for broken bones, and gamma rays are used to check for cancer. They are both very penetrating, but X-rays can be absorbed by bones. They are both also used to treat cancer
What is refraction?
Where light appears to change direction when passing through water or another medium. Waves can change direction when they change speed
What happens when waves slow down when entering another medium?
They bend towards the normal (line perpendicular to the medium). The opposite occurs when waves speed up. This causes the image of the object to change position
