# Physics Knowledge

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• Created by: allaiya
• Created on: 07-03-14 21:08
What is heat a measure of?
Energy (J)
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What happens when a substance is heated?
The particles gain kinetic energy and they move/vibrate faster
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What scale is heat measured on and why?
An absolute scale because it cannot go lower than 0
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What is temperature a measure of?
Hotness and the average kinetic energy of particles in a substance
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What is specific heat capacity? What is the equation?
The amount of energy needed to raise the temperature of a 1kg substance by 1 degree. Energy = mass x shc x temperature change
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How do substances boil?
Heat energy makes particles vibrate/move faster until the forces of attraction are overcome and big bubbles of gas form
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How do substances melt?
Heat energy makes particles vibrate/move faster until the forces of attraction are overcome and the particles begin to move around
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What is happening when there are flat spots on heating graphs?
The temperature is not being changed because the energy is being used to break intermolecular bonds between particles to change the state of the substance
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What is specific latent heat?
The amount of energy needed to change the state of a 1kg substance without changing the temperature
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What is the equation for specific latent heat?
Energy = mass x specific latent heat
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What is the conduction of heat a process of?
The process where vibrating particles pass on extra kinetic energy to neighbouring particles
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What does conduction occur in?
solid
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Why are metals good conductors of heat?
They have free electrons. Heating them makes electrons move faster and collide with other free electrons transferring energy
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What does convection occur in? When does convection occur?
Fluids (liquids and gases) When the more energetic particles move from the hotter region to the cooler region and take their heat energy with them
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What happens when fluids are heated?
They expand and become less dense
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What are convection currents?
When warmer less dense regions rise and cooler, more dense regions sink
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Doesnt need a medium (occur in a vacuum) Only occur in transparent substances
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How do microwaves heat food?
By microwaves Microwaves penetrate 1cm into water/fat molecules, increasing kinetic energy. Energy is conducted/convected to the centre
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What is the equation for payback time?
Payback time = initial cost / annual saving
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What is loft insulation?
When wool is laid across the loft floor to reduce conduction through the ceiling into the roof space
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What is cavity wall insulation?
When there is two layers of brick with air/form inside to reduce conduction/convection
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What is double glazing?
2 laers of glass with a gap of air to reduce conduction
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What is the equation for efficiency?
Efficiency = useful energy output / total energy input (x100)
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What is amplitude?
Displacement from rest to crest
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What is wavelength?
The length of a full cycle of wave
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What is frequency?
The number of complete waves passing by a point per second (Hz)
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What is the equation for wavespeed?
Wavespeed = frequency x wavelength
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What happens when waves hit an obstacle?
The direction can change by reflection, refraction and diffraction
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What happens when light is reflected from a) an uneven surface b) an even surface
a) Light reflects at different angles b) Light reflectes at same angle - Angle of incidence = angle of reflection
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When does total internal reflection occur?
When light rays travel through a dense material towards a less dense material
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What happens if the angle of incidence is a) less than critical angle? b) equal to critical angle? c) greater than critical angle?
a) Most of light refracted into outer layer, some internal reflection b) Ray goes along surface, quite a bit of internal reflection c) No light comes out = all international reflected
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What is diffraction?
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What is refraction?
When light changes speed as it passes from one medium to another
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What is the order of the electromagnetic spectrum?
Gamma High freq, short wavelength X-ray UV Visible light Infrared Microwaves Radio Low frequency, long wavelength
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What happens when electromagnetic radition is absorbed?
Heating and ionisation
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Are waves with higher frequencies or lower frequencies more dangerous and why?
Higher frequencies because they have more energy
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What is morse code?
What is morse code?
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How do optical fibres carry data?
Carry data over long distances as pulses of light or infrared radiation.
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What happens inside the optical fibre?
Waves enter at a greater angle than the criticle angle = total internal reflection Waves bounce off sides of the narrow core
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What are opital fibres used for?
Phone and internet Medical purposes (see inside body)
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What are the advantages of using optical fibres?
Digital = little interference Fast Multiplexing means lots of different signals can be transmitted down a single optical fibre at the same time = not many cables needed
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## Other cards in this set

### Card 2

#### Front

What happens when a substance is heated?

#### Back

The particles gain kinetic energy and they move/vibrate faster

### Card 3

#### Front

What scale is heat measured on and why?

### Card 4

#### Front

What is temperature a measure of?

### Card 5

#### Front

What is specific heat capacity? What is the equation?