Edexcel Physics: Optics
Terms in this set (33)
A change in wave speed when the wave moves from one medium to another, and hence there is a corresponding change in wave direction.
A measure of the amount of refraction caused by different materials; it is equal to the radio of the speed of light in a vacuum to the speed of light in the material.
The values of n1 and n2 are the refractive indices in each medium and the values of θ1 and θ2 are the angles that the ray makes to the normal to the interface between the two media, at the point the ray meets that interface.
How to measure the refractive index of a solid material
1. We can pass a beam of light through a block.
2. Measure the angle of incidence and the corresponding angle of refraction.
3. Take the refractive index of air to be 1.00.
4. Use the equation.
Where white light gets split into a rainbow of colours by a prism. The different wavelengths are refracted by different amounts.
Smaller wavelengths will be closer to the normal in the glass. When the light leaves, the smaller wavelengths will be further away from the normal in the air.
When waves pass from one medium into another...
Some wave energy will pass through and some will reflect. The proportion depends on the amount of refraction and the angle of incidence.
The largest angle of incidence that a ray in a more optically dense medium can have and still emerge into a less dense medium. Beyond this angle, the ray will be totally internally reflected.
Total internal reflection
This requires two conditions to be met:
1. The ray is attempting to emerge from the more dense medium.
2. The angle between the ray and the normal to the interface is greater than the critical angle.
Critical angle calculation
sinC = 1/n
Applications of TIR
1. Reflective signs
2. Fibre optics; a thin glass fibre can guide light along its length by the repeated TIR. This can be used to carry information, as decoration, or to guide sunlight or as a medical endoscope.
These converge parallel rays to a focus, at the focal length from the lens.
These diverge parallel rays to appear to have come from a virtual focus, at the focal length back from the lens.
These bring light rays closer together.
The point where rays incident on the lens and parallel to the principal axis will be made to meet by the refraction of the lens.
This spreads light rays further apart.
(of a diverging lens). This is the point where rays incident on the lens and parallel to the principal axis will appear to have come from on emergence from the lens.
The distance from the centre of a lens to its focal point.
Power of a lens
Power (dioptres) = 1/focal length
A diverging lens has a ? focal length
Therefore it has a negative power
For thin lenses in combination...
the overall power of the combination is equal to the sum of the individual powers of the lenses. P=P1+P2+P3+...
This can be projected onto a screen, and is on the other side of the lens from the object. This is common with convex lenses.
This can't be projected onto a screen, and is on the same side of the lens as the object. This is common with diverging lenses.
A numerical value given to measure the size comparison between image and original object.
Magnification= image size/object size or m=v/u
1/object distance + 1/image distance = 1/focal length
Real is positive. For virtual images, v is negative.
The orientation of the plane of oscillation of a transverse wave
The wave's oscillations occur in one single plane.
Field variations take place in all possible planes
These will transmit only the waves that are polarised in a particular plane.
What defines the plane of polarisation of electromagnetic waves?
The plane of the electric field's oscillations
How do you demonstrate that electromagnetic waves can be polarised?
1. There is a source of light.
2. The first filter only permits vibrations in its plane of polarisation.
3. The light is transmitted plane polarised.
4. The second filter is at 90 degrees to the first filter.
5. This blocks the polarised light so no light is transmitted.
Polarisation by reflection
When un polarised light reflects from a surface, the waves will become polarised. The degree of polarisation depends on the angle of incidence, but always tends towards a horizontal plane polarisation.
Polarisation by refraction
Light waves incident on a surface into which they can refract will reflect partially horizontally polarised light, and will also transmit partially vertically polarised light into the new medium.
Polarisation by chemical solutions
The amount of sugar solution varies the angle to which it rotates the polarisation of the light. Polarisation filters can be used to analyse the strength of the sugar solution by measuring he angle at which the light polarisation emerges after passing through the solution.