GCSE SCIENCESPhysics

LENS AND LIGHT

Refractive index measure of how much a substance can refract light

sin isin r

where i is air and r is from material

1sin c

where c is critical angle

Critical angle angle of incidence where refraction along the boundary

Total internal reflection occurs when angle of incidence in transparent substance is greater than critical

Real image screen, light rays meet

Converging lens in front of F -real, inverted and diminished

Back of F -virtual, upright and diminished

WORK, ENERGY AND FORCES

Moment Turning effect of a force

Weight of object is called load

Force applied is called effort

PressureForceArea

Liquids Virtually incompressible

Pressure is transmitted equally in all directions

Can be used as a force multiplier with bigger output area

ELECTROMAGNETISM

Motor effect Movement force, magnetic strength, size of current

Electromagnetic induction create p.d. using magnetic field

p.d. only induced while there is movement

movement speed, magnetic field strength, number of coils

Transformers Two coils of insulated wire on same iron core

When AC passes through primary, an alternating magnetic field is produced in the core

Field passes through the secondary coil and induces an alternating p.d.

p .d . primaryp .d . secondary

= pr imary turnssecondary turns

V p×I p=V s×I s

Chemistry

WATER

Hard water Calcium and magnesium salts

Get hardness from rocks or limestones

Ions react with soap form scum

Scale is formed when heated

Good for teeth and bones, reduce risk of heart disease

Softening Temporary hardness removed by heating

HCO3−¿¿

decompose form CO2

Calcium or magnesium react with carbon dioxide and form scale

Permanent hardness removed by Sodium Carbonate

Ion-exchange column

Treatment Sedimentation and filtration

Disinfection

Water filters –Carbon, ion-exchange resin, silver

CHEMICAL TESTS

Flame test Lithium Crimson

Sodium Yellow

Potassium Lilac

Calcium Red

Barium Green

Magnesium No colour

NaOH Iron (II) Green

Iron (III) Brown

Copper (II) Blue

Calcium White

Aluminium White (Dissolve with excess)

Magnesium White