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# Topic: Light

## 3.01 use the following units: degree (°), hertz (Hz), metre (m), metre/second (m/s) and second (s)

the units for:

angle = degree (°)

frequency = hertz (Hz)

wavelength = metre (m)

velocity = metre/second (m/s)

time = second (s)

2019-06-28T09:10:21+00:00Categories: 3 Waves, 3(a) Units, Edexcel iGCSE Physics, Uncategorized||

## 3.02 explain the difference between longitudinal and transverse waves

Transverse Waves:

• A wave that vibrates or oscillates at right angles (perpendicular) to the direction in which energy is transferred/ the wave is moving.
• g. Light

Longitudinal Waves:

• A wave that vibrates or oscillates at parallel to (along) the direction in which energy is transferred/ the wave is moving.
• g. Sound

## 3.03 know the definitions of amplitude, wavefront, frequency, wavelength and period of a wave

Key Definitions:

• Wavefront: Created by overlapping lots of different waves. A wavefront is where all the vibrations are in phase and the same distance from the source.
• Amplitude: The maximum displacement of particles from their equilibrium position.
• Wavelength: The distance between a particular point on one cycle of the wave and the same point on the next cycle.
• Frequency: The number of waves passing a particular point per second. Is measured in Hertz (Hz).
• Time Period: The time it takes for one complete wave to pass a particular point.

## 3.17 practical: investigate the refraction of light, using rectangular blocks, semi-circular blocks and triangular prisms

 1.       Set up your apparatus as shown in the diagram using a rectangular block. 2.       Shine the light ray through the glass block 3.       Use crosses to mark the path of the ray. 4.       Join up crosses with a ruler 5.       Draw on a normal where the ray enters the glass block 6.       Measure the angle of incidence and the angle of refraction and add these to your results table 7.       Comment on how the speed of the light has changed as the light moves between the mediums. 8.       Repeat this for different angles of incidence and different glass prisms.

## 3.19 practical: investigate the refractive index of glass, using a glass block

 1.       Set up your apparatus as shown in the diagram using a rectangular block. 2.       Shine the light ray through the glass block 3.       Use crosses to mark the path of the ray. 4.       Join up crosses with a ruler 5.       Draw on a normal where the ray enters the glass block 6.       Measure the angle of incidence and the angle of refraction and add these to your results table 7.       Calculate the refractive index 8.       Repeat steps 2 – 7 using a different angle of incidence 9.       Find an average of your results.

## 3.21 explain the meaning of critical angle c

Critical Angle:

• The angle of incidence which produces an angle of refraction of 900 (refracted ray is along the boundary of the surface).
• When the angle of incidence is greater than the critical angle, total internal reflection occurs (all light is reflected at the boundary).
• This effect only occurs at a boundary from a high refractive index material to a low refractive index material.
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Section 1: Principles of chemistry

a) States of matter

b) Atoms

c) Atomic structure

d) Relative formula masses and molar volumes of gases

e) Chemical formulae and chemical equations

f) Ionic compounds

g) Covalent substances

h) Metallic crystals

i) Electrolysis

Section 2: Chemistry of the elements

a) The Periodic Table

b) Group 1 elements: lithium, sodium and potassium

c) Group 7 elements: chlorine, bromine and iodine

d) Oxygen and oxides

e) Hydrogen and water

f) Reactivity series

g) Tests for ions and gases

Section 3: Organic chemistry

a) Introduction

b) Alkanes

c) Alkenes

d) Ethanol

Section 4: Physical chemistry

a) Acids, alkalis and salts

b) Energetics

c) Rates of reaction

d) Equilibria

Section 5: Chemistry in industry

a) Extraction and uses of metals

b) Crude oil

c) Synthetic polymers

d) The industrial manufacture of chemicals