Physics: EM Spectrum and Waves

Wave speed formula

frequency * wavelength

time period

1/frequency

Wavelength

the distance between two peaks or two troughs of a wave.

Amplitude

the half height of a wave: the distance between the equilibrium position and the point of maximum displacement.

Frequency

the number of waves per second. It is measured in Hertz, Hz.

Time period

 how long it takes a wave to complete a whole cycle.

Longitudinal

a wave whose oscillations are parallel to the direction of travel of a wave.

Transverse

a wave whose oscillations are perpendicular to the direction of travel of a wave.

Wave Speed

the speed at which energy is transferred through the medium

Absorb

when a wave is absorbed by a substance

Transmit

 a wave passing through a substance

Refract

the change of direction of a wave as it passes across a boundary

Reflection

the change of direction of a wave at a boundary.

Sieverts

unit of radiation dose

order of Em Spectrum

Radio, Micro, Infra-red, Visible, Ultraviolet, X-rays, Gamma Rays

What can radio waves be used for?

Radio, Tv Broadcasts, Mobile phone signals, Bluetooth

How does a radio transmitter and receiver work?

Produced by oscillations in electrical circuits. Transmitted through the air. Radio waves are absorbed by receiver aerials where they induce an alternating current, which causes oscillations in the receiver. The frequency of oscillations in the receiver is the same as the frequency of the

Microwave uses

Heat up food

How can microwaves heat up food?

Microwaves penetrate the food. The energy is absorbed by the water molecules inside the food, makes the water molecules vibrate and causes the water molecules to get hot. The energy is then transferred from the water to the rest of the food.

What are the dangers of exposure to microwaves?

Exposure to high levels of microwaves can cause burns, cataracts, and other health issues. Microwaves can also interfere with electronic devices and communication systems.

Perfect black body

An object the absorbs all radiation that falls on it and it would not reflect, or transmit any radiation.

Black Body radiation

An object that has a constant temperature emits radiation across a continuous range of wavelengths.

What would happen if the world had no atmosphere?

The temperature at the surface would drop to -180 degrees at night because the surface would not be absorbing any radiation from the sun, but reflecting radiation into space.

What would happen if the world had no atmosphere? (infra-red)

Some gases in the atmosphere (water, methane) emit longer wavelength infrared radiation from the earth and prevent it from escaping into space. This process makes the earth colder than it would be if these gases were not present in its atmosphere.

Safety risks for UV light

Don’t point UV light directly onto your skin/eyes. Don’t use an invisible ink pen on your skin because it can absorb even more UV light and cause skin cancer.

What can UV light be used for?

Invisible ink, security measures, tanning salons, curing chemicals.

Safety precautions to take when using UV

Sunglasses, sunscreen.

How does X-Ray imaging work?

X rays are passed through the skin and are transmitted into the body. When X-Rays reah the photographic film, they expose it turning it grey. When X-Rays hit a bone, they are absorbed.