# Physics Unit 1 OCR (For the new syllabus)

These are just some revision notes for OCR Physics Unit 1 21st century. This is for the new syllabus

• Created by: Angela
• Created on: 11-11-17 17:15

## Basic Atomic Structure

Atoms:

• 3 parts - Protons - positive charge , Neutrons - neutral charge, Electrons - negative charge
• They can undergo physical change
• Mostly empty space
• Atomic Number = Proton and electron number
• Atomic Mass = Proton + neutron number
• Proton  (Charge = +1) (Mass = 1)
• Neutron (Charge = neutral) (Mass = 1)
• Electron (Charge = -1) (Mass = 1/2000)

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## Law of Reflection

Keywords

• Incident Ray: The light ray going into the mirror
• Reflected ray: The light ray that comes back of the mirror
• Normal: A dotted line at 90 degrees to the mirror. We measure angle from this reference point

Angle of Incidence = Angle of Reflection

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## Refraction

"Sound waves and light waves change speed when they pass across the boundary between two substances with different densities, such as air and glass. This causes them to change direction and this effect is called refraction.

There is one special case you need to know. Refraction doesn't happen if they cross the boundary at an angle of 90° - in that case they carry straight on.

Remember that sound and light waves behave just like water waves in a ripple tank. The bending follows a regular pattern. Check your understanding of refraction by having a go at the animation."  - GCSE Bitesize

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## Dispersion

When white light passes through a prism, it is dispersed and the different colours of the spectrum separate. Dispersion causes rainbows. Dispersion happens because the different spectral colours travel at the same speed in a vacuum, but at different speeds in a medium such as glass. The amount of bending increases as the change in wave speed increases. It also increases as the refractive index increases. - GCSE Bitesize

The spetral colours in order of decreasing wavelength are: Red Orange Yellow Green Blue Indigo Violet

"For dispersion in a medium such as glass: each spectral colour has a different refractive index, blue light has a greater refractive index in a given medium than red light, blue light refracts (bends) more than red light" - GCSE Bitesize

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## Parts of a Wave

• Wavelength: The length of one complete wave
• Frequency: The number of waves per second (Hz - Hertz)
• Amplitude: The hight of the wave from a central point

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## Longitudinal and Transverse

Longitudinal Wave: The vibrations are along the same direction as the direction of travel

Transverse: Vibration is perpendicular (90 degrees) to the direction of travel.

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## The Wave Equation

Wave speed = Frequency x wavelength

c(m/s)      =    f (Hz)      x     (m)

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## Standard Form Abbreviations

• Tera      x10^12
• Giga      x10^9
• Mega     x10^6
• Kilo        x10^3
• Milli       x10^-3
• Micro    x10^-6
• Nana    x10^-9
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## The EM spectrum

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• Radiation can be imagined as a strea of particles called photons
• Photon are little packets of energy
• The energy is linked to the frequency

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## Ionisation

Ionisation occurs when an atom is hit by high energy photons. They knock electrons of the atom

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## Microwaves

Protection from Microwaves

• Metal cases and door screens protect user from radiation
• The radiation is reflected dack inside

They can penetrate glass and plastics but are reflected off metal

They can also penetrate body tissues causeing water mlecules in the body to heat up, This can lead to blood becoming overheated and can result in killing cells

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Radio , Microwave, Infrared, Ultraviolet, X-rays, Gmma

Ionising Radiation causes cancer in humans. U-V, X-rays and Gamma radiation have enough energy to ionise.

The packets of energy in radiation are called photons

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## Climate Change

The greenhouse effect is the name given to the natural process that causes the Earth to be warmer than it would be in the absence of an atmosphere.Greenhouse gases are produced naturally and trap heat in the Earth’s atmosphere, like a blanket. Water vapour is the largest contributor, responsible for 98 per cent of the natural greenhouse effect. Global warming is attributed to the enhanced greenhouse effect. This is caused by the increased concentration and effect of greenhouse gases, such as carbon dioxide, methane and fluorocarbons. When fossil fuels are burned in power stations, vehicles, industry or homes, greenhouse gases enter the atmosphere. Although these gases have always been present in the world's atmosphere their concentration is increasing as more and more fossil fuels are burned

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## Speed of Sound

Speed = distance/time

The speed of sound in air is 340m/s

Sound travels faster in solids because the particles are closer together meaning the vibrations can travel along faster

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## Power and Energy Calculations

Energy = Power x Time

Efficiency = (Useful energy out/total energy in)x100

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## S and P waves

S and P waves are 2 types of seismic waves

P waves (P - push and pull) - longitudinal

S waves (S - sideways) - transverse

P waves can travel through solids and liquids (like sound waves) but s-waves can only travel through solids.

P waves are also faster

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