# Physics Unit 1

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Physics Unit 1

## 2. Heating and Cooling

### 2.1. Convection

2.1.1. Heated particles take up a greater volume. The gap between particles widen.

2.1.2. In hot areas the fluid is less dense than in cold areas.

### 2.2. Conduction

2.2.1. Free electrons

2.2.1.1. Charged ions with kinetic energy move from hot to cold.

2.3.1. Passes through vacuum.

2.3.2. Objects emit and absorb radiation.

2.3.3. Light, shiny surfaces reflect heat whereas dark, matt surfaces absorb and emit it.

### 2.4. Factors affecting the rate of...

2.4.1. Condensation

2.4.1.1. Decrease in temperature increases rate

2.4.2. Evaporation

2.4.2.1. Increase in temperature increases rate

2.4.2.2. Increase in surface area increases rate

2.4.2.3. Air moving over the surface increases rate

## 3. Mains electricity

### 3.1. The National Grid

3.1.1. Step-up transformers

3.1.1.1. High voltage transmission lines

3.1.1.1.1. Step-down transformers

3.1.2. Voltages

3.1.2.1. Power Stations produce electricity at 25,000V

3.1.2.2. Step-up transformer

3.1.2.2.1. Power lines

3.1.2.3. Household electricity is about 230V

## 4. Waves

### 4.1. General properties of waves

4.1.1. Transverse waves have their oscillations or vibrations at right angles to the direction of travel and energy transfer. An example of these waves are light waves.

4.1.2. Longitudinal waves have their oscillations along the same direction as the direction of travel and energy transfer. An example of these are sound waves and waves of a stretched spring.

4.1.3. Refraction: sound and light waves change speed when they move across substances with different densities which in turn causes them to change direction. Refraction doesn't happen if the waves cross the boundary at an angle of 90° (called the normal) - in that case they carry straight on.

4.1.4. Diffraction: when waves meet a gap in a barrier, they carry on through the gap. Though the waves do spread out to some extent beyond the gap. This is dependent on how the width of the gap compares to the wavelength of the waves.

4.1.5. Reflection: sound and light waves reflect from surfaces. When this happens, they obey the law of reflection: angle of incidence = angle of reflection. Link contains more context. Also, see ray diagrams.

### 4.2. Sound and light

4.2.1. When an object (or substance) vibrates, it produces sound. Greater the amplitude, louder the sound. Greater the frequency, higher the pitch.

## 5. Origins of the Universe

### 5.1. Doppler effect

5.1.1. High pitched: source moves towards observer

5.1.1.1. Frequency increase and wavelength decreases

5.1.2. Low pitched: source moves away from observer

5.1.2.1. Frequency decreases and wavelength increases

### 5.2. Red-Shift

5.2.1. The further away a star is the more its light has red-shifted

5.2.2. The absorption spectrum of a star has black lines to show where helium absorbs the light.

5.2.2.1. In a distant star, the black lines are closer to red part of the spectrum. This shows how far a star moves away from us.