Q1 → What can happen when a wave encounters a boundary between two different materials?
A → When a wave reaches a boundary between two different materials, three things can happen:
The wave can be absorbed by the new material.
The wave can be reflected at the boundary.
The wave can be transmitted, meaning it travels into the new material.
What actually happens depends on the wavelength of the wave and the properties of the materials involved.
Q2 → What is absorption of a wave?
A → Absorption occurs when a wave transfers its energy to the material it is trying to cross into. The wave’s energy is transferred to the material’s energy stores. Often this transferred energy becomes thermal energy, causing the material to heat up.
Q3 → How do microwaves demonstrate absorption?
A → In a microwave oven, microwaves are absorbed by water molecules in food (for example, a potato). The water molecules vibrate when they absorb the microwaves. This vibration increases their thermal energy. The thermal energy then conducts through the rest of the potato, causing its overall temperature to increase.
Q4 → What is transmission of a wave?
A → Transmission occurs when a wave continues to travel through a new material after crossing a boundary. The wave carries on moving through the second material. Transmission often leads to another process called refraction.
Q5 → What is reflection of a wave?
A → Reflection occurs when a wave bounces back at the boundary between two media instead of passing through. Waves such as light and sound can be reflected at the boundary between two different materials.
Q6 → What is an example of reflection in everyday life?
A → The reflection of sound produces echoes. Light reflection allows us to see objects. Visible light waves from a light source reflect off objects and enter our eyes, enabling vision.
Q7 → How does the shininess of an object affect reflection of visible light?
A → The shinier an object is, the better it reflects visible light. For example, mirrors reflect light very effectively because they have smooth, shiny surfaces.
Q8 → What is the law of reflection?
A → The law of reflection states that:
Angle of incidence = Angle of reflection.
This applies to all reflected waves.
Q9 → How are the angles of incidence and reflection defined (Source 1 definition)?
A → The angle of incidence is the angle between the surface and the incident ray.
The angle of reflection is the angle between the surface and the reflected ray.
Q10 → How are the angles of incidence and reflection defined (Source 2 and 3 definition)?
A → The angle of incidence is the angle between the incident ray and the normal.
The angle of reflection is the angle between the reflected ray and the normal.
All angles are measured between the ray and the normal (the imaginary line at right angles to the surface).
Q11 → What is the normal in reflection and refraction diagrams?
A → The normal is an imaginary line drawn perpendicular (at 90°) to the surface at the point of incidence (where the wave hits the boundary). It is often shown as a dotted line. All angles are measured relative to this line.
Q12 → Give a numerical example of the law of reflection.
A → If a light ray strikes a surface at 32° to the normal, it will be reflected at 32° to the normal.
Q13 → What is a ray in wave diagrams?
A → A ray is a straight line showing the direction or path a wave travels in. Rays are always drawn as straight lines and are perpendicular to the wavefronts.
Q14 → What are wavefronts?
A → Wavefronts are lines representing the peaks of waves. Each line in a wavefront diagram shows the position of a wave peak.
Q15 → What does the distance between wavefronts represent?
A → The distance between successive wavefront lines represents the wavelength of the wave.
Q16 → What is refraction?
A → Refraction is the process by which a wave changes speed and sometimes direction when it crosses a boundary between two materials with different densities. This usually happens at a boundary between transparent materials such as air and glass.
Q17 → What causes refraction to occur?
A → Refraction occurs because different materials have different densities, and density affects how fast waves travel through a material. When a wave enters a material where it travels at a different speed, its direction may change.
Q18 → What is optical density?
A → Optical density is a measure of how quickly light can travel through a material. The higher the optical density, the slower light waves travel through that material.
Q19 → How does density affect wave speed?
A → In general, the denser (or more optically dense) a transparent material is, the more slowly light travels through it. For example, glass is denser than air, so light travels more slowly in glass than in air.
Q20 → What happens when a wave travels from a less dense medium to a more dense medium?
A → When a wave travels from a less dense medium to a more dense medium:
Its speed decreases.
Its wavelength decreases.
Its frequency stays the same.
If it enters at an angle, it bends towards the normal.
The wavefronts become closer together, showing a shorter wavelength.
Q21 → What happens when a wave travels from a more dense medium to a less dense medium?
A → When a wave travels from a more dense medium to a less dense medium:
Its speed increases.
Its wavelength increases.
Its frequency stays the same.
If it enters at an angle, it bends away from the normal.
Q22 → Why does frequency stay the same during refraction?
A → The frequency remains constant because it is determined by the source of the wave. When the speed changes at a boundary, the wavelength changes accordingly, but the frequency does not change.
Q23 → What is the relationship between wave speed, frequency, and wavelength?
A → The relationship is given by the equation:
Wave speed = frequency × wavelength
This means that for a given frequency, wavelength is proportional to wave speed.
Q24 → What happens to wavelength when a wave slows down?
A → If a wave slows down, its wavelength decreases. This is because wave speed equals frequency multiplied by wavelength, and the frequency remains constant.
Q25 → What happens to wavelength when a wave speeds up?
A → If a wave speeds up, its wavelength increases, since frequency remains constant.
Q26 → What happens if a wave crosses a boundary along the normal?
A → If a wave travels along the normal (perpendicular to the boundary), it will change speed when entering a new material, but it will not change direction. Therefore, it is not refracted.
Q27 → What happens when light enters glass perpendicularly from air?
A → When light enters glass perpendicularly (along the normal), it does not bend. It passes straight through. However, its speed decreases and its wavelength decreases, while its frequency remains the same.
Q28 → What happens when light enters a denser medium at an angle?
A → When light travels from a low-density medium (such as air) into a high-density medium (such as glass) at an angle:
Its speed decreases.
Its wavelength decreases.
Its frequency remains the same.
The ray bends towards the normal.
The angle of refraction is smaller than the angle of incidence.
Q29 → What happens when light leaves a denser medium at an angle?
A → When light travels from a high-density medium (glass) into a low-density medium (air) at an angle:
Its speed increases.
Its wavelength increases.
Its frequency remains the same.
The ray bends away from the normal.
The angle of refraction is larger than the angle of incidence.
The ray is bent back into its original direction as it leaves a rectangular block.
Q30 → How can refraction be explained using wavefronts?
A → When a wave travels from air into glass at an angle, the part of the wavefront that enters the denser medium first slows down before the rest. For example, the bottom of the wavefront slows first while the top continues at a higher speed and travels further. This difference in speed across the wavefront causes the wave to change direction.
Q31 → How does refraction cause optical illusions?
A → Refraction can cause optical illusions because the refracted light waves appear to come from a different position than their actual source. This happens because the direction of the light changes at the boundary.
Q32 → What does the mnemonic “FAST” mean in refraction?
A → “FAST” stands for:
Faster – Away
Slower – Towards
This means that when a wave speeds up, it bends away from the normal. When a wave slows down, it bends towards the normal.
Q33 → How do you construct a ray diagram for reflection?
A →
Draw the boundary surface.
Draw the normal at 90° to the surface at the point of incidence.
Draw the incident ray meeting the normal.
Measure the angle of incidence between the incident ray and the normal.
Draw the reflected ray so that the angle of reflection equals the angle of incidence.
Q34 → How do you construct a ray diagram for refraction?
A →
Draw the boundary between the two materials.
Draw the normal at 90° to the boundary.
Draw the incident ray meeting the normal at the boundary. The angle between the incident ray and the normal is the angle of incidence (use a protractor if given a value).
Draw the refracted ray in the second medium.
If the second material is more optically dense, the refracted ray bends towards the normal and the angle of refraction is smaller than the angle of incidence.
If the second material is less optically dense, the refracted ray bends away from the normal and the angle of refraction is larger than the angle of incidence.
Source 1: When a WAVE encounters a boundary between two materials, it can do one of three things: 1. ABSORPTION:
Here, the wave TRANSFERS its ENERGY to the second material. Often, this turns into THERMAL ENERGY, causing the material to heat up. For example in a MICROWAVE OVEN the MICROWAVES get ABSORBED by the water molecules in the potato, causing them to VIBRATE and heat up. This THERMAL ENERGY conducts through the rest of the potato, causing its temperature to INCREASE.
- REFLECTION: Reflection occurs when the wave BOUNCES BACK at the boundary of the two media.
The SHINIER an object, the BETTER it reflects visible light. (For example, light reflects off of mirrors).
This allows us to SEE objects. The visible light waves given off by a light source REFLECT off other objects, and enter our eyes.
Ray diagrams include a VIRTUAL line known as the NORMAL which is PERPENDICULAR to the surface of reflection. The ANGLE OF INCIDENCE is the angle between the SURFACE and the INCIDENT RAY.
The ANGLE OF REFLECTION is the angle between the SURFACE and the REFLECTED RAY. Whenever reflection occurs on a surface, the ANGLE OF INCIDENCE is EQUAL to the ANGLE OF REFLECTION. ||| 3. TRANSMISSION:
The wave continues to TRAVEL THROUGH the new material. This can lead to another process known as REFRACTION.
Refraction
REFRACTION happens when a wave crosses into a new medium, causing it to change SPEED and sometimes DIRECTION.
When the wave travels from a LESS DENSE medium to a MORE DENSE medium, the SPEED and the WAVELENGTH of the wave DECREASE but the FREQUENCY of the wave STAYS THE SAME.
When the wave travels from a MORE DENSE medium to a LESS DENSE medium, the SPEED and the WAVELENGTH of the wave INCREASE but again the FREQUENCY of the wave STAYS THE SAME.
We can show this using LIGHT waves travelling through AIR (less dense) and GLASS (more dense). ||| E.g. Light entering perpendicularly
When the light enters the glass PERPENDICULARLY, it does NOT bend - it just passes STRAIGHT THROUGH. In wavefront diagrams, each LINE, known as WAVEFRONTS, represents the PEAK of a wave.
The DISTANCE between each line is the WAVELENGTH of the wave. When light travels from air into a denser medium like glass, its speed decreases and its wavelength decreases, while its frequency stays the same.
Conversely, when light moves from a high-density medium like glass back into a lower-density medium like air, its speed increases and its wavelength increases, though the frequency remains constant. In this context, wavefronts represent the peaks of the wave, and the distance between them defines the wavelength. ||| E.g. Light entering at an angle
If the waves enters the new medium AT AN ANGLE, the DIRECTION of the wave will CHANGE: When a light wave travels from a low-density medium (air) to a high-density medium (glass), its speed decreases, its wavelength decreases, and the ray bends towards the normal, while its frequency stays the same.
Conversely, when the light wave travels from a high-density medium (glass) back into a low-density medium (air), its speed increases, its wavelength increases, and the ray bends away from the normal, though the frequency again stays the same. When the wave travels from a LESS DENSE medium to a MORE DENSE medium, the WAVE bends TOWARDS the NORMAL (a line perpendicular to the surface).
When the wave travels from a MORE DENSE medium to a LESS DENSE medium, the WAVE bends AWAY from the NORMAL.
This can be explained using WAVEFRONTS: When a wave travels from air into glass, the bottom of the wavefront enters the denser medium first and slows down, while the top of the wave continues at a faster speed and travels further, causing the entire wave to change direction. ////////// Source 2: Reflection of waves
Waves - including sound and light - can be reflected at the boundary between two different materials. The reflection of sound causes echoes.
The law of reflection states that: angle of incidence (angle between the normal and the incident ray) = angle of reflection (angle between the reflected ray and the normal (the imaginary line drawn at 90 degrees to the reflecting surface))
For example, if a light ray hits a surface at 32°, it will be reflected at 32°.
The
angles of incidence and reflection are measured between the light ray and the
normal - an imaginary but useful line at right angles to the boundary/surface between air/glass. All angles are measured to this line. The diagrams show a water wave being reflected at a barrier, and a light ray being reflected at a plane (a flat, two-dimensional surface) mirror. ||| Refraction of waves:
Different materials have different densities. Light waves may change direction at the boundary between two transparent materials.
Refraction is the process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium (at a boundary), eg a light ray changes direction when refracted by a lens. It is important to be able to draw ray diagrams to show the refraction of a wave at a boundary. Refraction can cause optical illusions as the light waves appear to come from a different position to their actual source.
Explaining refraction - Higher:
The density of a material affects the speed that a wave will be transmitted (when a wave is passed across or through a material (medium)) through it. In general, the denser the transparent material, the more slowly light travels through it. Glass is denser than air, so a light ray passing from air into glass slows down. If the ray meets the boundary at an angle to the normal, it bends towards the normal. The reverse is also true. A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle. The wave slows and its wavelength decreases as it enters the glass. As the wave returns to air,
its speed and wavelength increase to their original values. If the light ray hits the block at an angle its speed and direction changes. The ray is bent back into its original direction as it leaves the block. As the ray goes into the glass from the air, it is bent towards the normal. The angle of refraction is less than the angle of incidence. A useful way of remembering the speed and direction changes of light during refraction is ‘FAST’: Faster - Away / Slower - Towards. ||| Wave speed, frequency and wavelength in refraction:
For a given
frequency of light, the wavelength is proportional to the wave speed:
wave speed = frequency × wavelength
So if a wave slows down, its wavelength will decrease. The effect of this can be shown using wave front diagrams like the one below. The diagram shows that as a wave travels into a denser medium, such as water, it slows down and the wavelength decreases. Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter. So, in a diagram, the right hand side of the incoming wave slows down before the left hand side does. This causes the wave to change direction. ////////// Source 3: All Waves Can be Absorbed, Transmitted or Reflected:
When waves arrive at a boundary between two different materials, three things can happen:
1) The waves are absorbed by the material the wave is trying to cross into - this transfers
energy to the material’s energy stores (this is how microwaves work).
2) The waves are transmitted - the waves carry on travelling through the new material.
This often leads to refraction.
3) The waves are reflected - more on this below.
What actually happens depends on the wavelength of the wave and the properties of the materials involved.
You Can Draw a Simple Ray Diagram for Reflection:
1) There’s one simple rule to learn for all reflected waves:
Angle of incidence = Angle of reflection
2) The angle of incidence is the angle between
the incoming wave and the normal.
3) The angle of reflection is the angle between
the reflected wave and the normal.
4) The normal is an imaginary line that’s perpendicular
(at right angles) to the surface at the point of incidence
(the point where the wave hits the boundary).
5) The normal is usually shown as a dotted line.
A ray is a line showing the path a
wave travels in. It’s perpendicular to a
wave’s wave fronts. Rays
are always drawn as straight lines. ||| Refraction -Waves Changing Direction at a Boundary
1) When a wave crosses a boundary between materials at an angle it changes direction - it’s refracted.
2) How much it’s refracted by depends on how much the wave speeds up or slows down, which usually depends on the density of the two materials (usually the higher the density of a material, the slower a wave travels through it). If a wave crosses a boundary and slows down it will bend towards the normal.
If it crosses into a material and speeds up it will bend away from the normal.
3) The wavelength of a wave changes when it is refracted, but the frequency stays the same.
4) If the wave is travelling along the normal it will change speed, but it’s NOT refracted. ||| When going from a less dense to a denser medium, the wave fronts are now closer together, which shows a change in wavelength (and so a change in velocity), and the wave hits a different medium at an angle, so the wave changes direction. ||| 5) The optical density of a material is a measure of how quickly light can travel through it - the higher the optical density, the slower light waves travels through it. ||| You can construct a ray diagram for a refracted light ray.
1) First, start by drawing the boundary between your two materials and
the hormal (a line that is at 90° to the boundary).
2) Draw an incident ray that meets the hormal at the boundary.
The angle between the ray and the hormal is the angle of incidence.
(If you’re given this angle, make sure to draw it carefully with a protractor.)
3) Now draw the refracted ray on the other side of the boundary.
If the second material is optically denser than first, the refracted ray bends towards
the hormal (like on the right). The angle between the refracted ray and the hormal
(the angle of refraction) is smaller than the angle of incidence. If the second material
is less optically dense, the angle of refraction is larger than the angle of incidence.
Q1 → What can happen when a wave encounters a boundary between two different materials?
A → When a wave reaches a boundary between two different materials
three things can happen:
The wave can be absorbed by the new material.
The wave can be reflected at the boundary.
The wave can be transmitted
meaning it travels into the new material.
What actually happens depends on the wavelength of the wave and the properties of the materials involved.
Q2 → What is absorption of a wave?
A → Absorption occurs when a wave transfers its energy to the material it is trying to cross into. The wave’s energy is transferred to the material’s energy stores. Often this transferred energy becomes thermal energy
causing the material to heat up.
Q3 → How do microwaves demonstrate absorption?
A → In a microwave oven
microwaves are absorbed by water molecules in food (for example
Q4 → What is transmission of a wave?
A → Transmission occurs when a wave continues to travel through a new material after crossing a boundary. The wave carries on moving through the second material. Transmission often leads to another process called refraction.
Q5 → What is reflection of a wave?
A → Reflection occurs when a wave bounces back at the boundary between two media instead of passing through. Waves such as light and sound can be reflected at the boundary between two different materials.
Q6 → What is an example of reflection in everyday life?
A → The reflection of sound produces echoes. Light reflection allows us to see objects. Visible light waves from a light source reflect off objects and enter our eyes
enabling vision.
Q7 → How does the shininess of an object affect reflection of visible light?
A → The shinier an object is
the better it reflects visible light. For example
Q8 → What is the law of reflection?
A → The law of reflection states that:
Angle of incidence = Angle of reflection.
This applies to all reflected waves.
Q9 → How are the angles of incidence and reflection defined (Source 1 definition)?
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Energy Stores and Transfers, Open and Closed Systems36
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Examples of Energy Transfers, Energy Flow Diagrams13
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Calculation of Energy Changes, Conservation of Energy11
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Energy Dissipation, Reducing Unwated Energy Transfers in the Home13
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Conduction and Convection112
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Specific Heat Capacity, Intro to Thermal Conductivity22
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Required Practical: Specific Heat Capacity20
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Power124
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Required Practical: Investigating Insulation121
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Efficiency108
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Types of Energy Resources290
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Trends and Uses of Energy Resources, Energy for Transport and Heating246
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Charge and Current82
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Current, Potential Difference & Resistance58
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Required Practical: Investigating Resistance89
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Resistors and I-V Graphs132
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Required Practical: I-V Graphs99
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Series and Parallel Circuits55
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Direct and Alternating Current31
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Mains Electricity78
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Electrical Power25
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Electrical Energy Transfers and Power Ratings71
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The National Grid84
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Static Electricity and Sparks77
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Electric Fields and Sparks75
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Density - Intro13
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Required Practical: Density17
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States of Matter36
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Internal Energy35
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Specific Latent Heat, Heating & Cooling Graphs (and recap of Internal Energy)36
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Particle Motion in Gases, Gas Pressure & Temp, Boyle's Law, Work Done on Gases41
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Atomic Structure, Radioactive Decay, Types of Radiation, Intro to G-M Tube75
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Nuclear Equations, Half Life, Contamination, Irradiation, Peer Reviewing79
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Background Radiation, Correct Count-Rate, Uses and Risks of Radiation45
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Nuclear Fission and Fusion97
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Scalars and Vectors24
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Contact and Non-Contact Forces71
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Gravity, Weight & Centre of Mass97
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Resultant Forces, Scale Drawings, & Components of a Force113
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Work Done and Its Energy Transfers53
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Forces and Elasticity112
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Required Practical: Force and Extension118
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Moments, Levers and Gears101
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Pressure in Fluids118
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Upthrust and Atmospheric Pressure67
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Distance and Displacement17
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Speed and Velocity25
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Distance-Time Graphs24
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Acceleration106
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Velocity-Time Graphs61
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Terminal Velocity121
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Newton's First Law and Inertia61
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Newton's Second Law and Inertial Mass51
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Newton's Third Law73
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Required Practical: Force, Mass and Acceleration137
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Stopping Distance and How Braking Works131
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Momentum and Changes in Momentum104
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Vehicle Safety Features40
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Transverse & Longitudinal Waves36
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Wave Period & Speed, Measuring the Speed of Sound in Air23
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Required Practical: Measuring Waves in a Ripple Tank19
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Required Practical: Measuring Waves on a String9
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Sound Waves and Human Hearing101
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Using Ultrasound for Imaging and Detection70
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Using Seismic Waves for Exploration81
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Intro to Electromagnetic Waves, Intro to Visible Light92
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Uses of Radio Waves91
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Uses of Microwaves25
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Uses of Infrared Radiation33
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Uses of Visible Light21
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Uses of Ultraviolet Radiation25
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Uses of X-Rays and Gamma Rays27
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Dangers of Electromagnetic Waves63
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Visible Light and Colour Filters137
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Required Practical: Investigating Infrared Radiation75
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Reflection and Refraction114
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Specular and Diffuse Reflection61
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Required Practical: Reflection and Refraction119
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Lenses and Ray Diagrams153
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Black Body Radiation and Earth’s Temperature169
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Magnetism and Types of Magnets28
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Magnetic Fields30
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Electromagnetism, The Right Hand Grip Rule and Solenoids40
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The Motor Effect55
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Fleming's Left Hand Rule41
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Electric Motors and Loudspeakers25
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Induced Potential, The Generator Effect and Microphones52
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Transformers and their Equations137
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Our Solar System and Orbital Motion184
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The Life Cycle of Stars100
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Red Shift and The Big Bang81
