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Physics (Electrostatics (Subatomic particle charge (Proton: 1, Electron: …
Physics
Electrostatics
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Insulators = charges cannot move e.g. wood, plastic
Conductors = charges can move e.g. metals, graphite, electrolytes1
Like charges repel (+/+, -/-)
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Rubbing 2 insulators together results in the transfer of electrons between surface atoms. This is one method of charging an object.
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Reflection
Laws of Reflection
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The incident ray, reflected ray and the normal all lie in the same plane
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Electricity
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Kirchhoff's Laws
Kirchhoff's 1st Law
Charge cannot be created or destroyed (Conservation of Charge). As current = “rate of flow of charge” it therefore follows that we cannot “create or destroy” current.
Kirchhoff’s 1st Law states: “...the sum of currents entering a junction or component is equal to the sum of currents exiting that junction or component...”
From Kirchoff’s 1st Law we see that current is not “used up” – the same amount of current exits a component as enters.
Rectilinear Propagation
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Sources and shadows
A Source is something which emits light. It will either produce it’s own light (eg. Sun) or reflect the light of something else (eg. Moon)
A point source is a luminous object which is very small compared with the other objects considered: e.g a small LED or tiny filament torch.
Produces clear, sharp-edged shadows called the umbra.
An extended source is one which is not small – usually it extends in one direction. e.g a large filament lamp or fluorescent tube.
Produces an area beside the umbra where light from some parts of the source can reach, called the penumbra.
Pinhole cameras
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If we move the object closer, the image gets larger
If we make the pinhole larger, the image gets brighter but blurrier
Refraction
It is when light travels from one medium to another, it’s speed changes and hence it changes direction
When it slows down (e.g. Air to Glass) it changes direction towards the normal, and vice-versa when speeding up.
The speed of light in a material compared with its speed in a vacuum is called the material’s refractive index
Total Internal Reflection occurs when light is travelling from a medium of higher refractive index to lower (i.e. speeds up, e.g. glass to air), and the Angle of Incidence > Critical Angle
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Force
A force is an interaction between 2 bodies that causes a change in an object’s motion (either speed and/or direction) and/or shape
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Weight is the force due to the gravitational attraction of our planet. It is given by the following formula:
Weight (N) = Mass (kg) x Gravitational Field Strength (m/s2) (W = m x g)
Pressure is a measured of the force exerted per unit area. Formula: Pressure (Pa) = Force (N)/Area (m2)
Springs
Hooke's Law
F = K x X
On a graph, this would look like a straight line
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