# (b) Mains electricity

## 2.02 understand how the use of insulation, double insulation, earthing, fuses and circuit breakers protects the device or user in a range of domestic appliances

Fuses Stop the flow of current by melting if the current is too high. So protecting sensitive components and people because if the components function at too higher temperature it can cause a fire.

Circuit breakers again break the circuit if current is too high.

Insulation and double insulation prevent people from touching exposed wires and getting shocks.

Earthing provides a low resistance path to the earth so if some one does come into contact with a current instead of flowing through them to the earth giving them a shock it flows through the earthing wire.

## 2.03 understand why a current in a resistor results in the electral transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts

 Resistance causes transfer of electrical energy to heat energy. Some components are designed to have a high resistance to make sure this happens, for example electrical heaters that have lots of resistors to ensure a high resistance so a lot of heat is produced.

## 2.04 know and use the relationship between power, current and voltage: and apply the relationship to the selection of appropriate fuses

power (w) = current (A) x voltage (V)

when looking at a circuit a component will be given a power and a voltage appropriate to run at then the current can be calculated so the rating of the fuse can be selected for slightly higher than that.

## 2.06 know the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery

AC is constantly changing magnitude and direction. AC is how mains electricity is produced from turbines.

DC is constant. And is produced from a battery and used in some sensitive components like in computing.

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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