Static Electricity

1. The study of static electricity is called electrostatics.
2. Static electricity is electric charge that is at rest or not moving.
3. There are two types of static electric charges, i.e. positive charges and negative charges.
4. Positive charges consist of protons. Protons do not move.
5. Negative charges consist of electrons. Electron transfer happens when two different materials are rubbed together.

Types of static electric charges and their properties

1. Charges of the same type (like charges) repel one another.
2. Charges of different types (unlike charges) attract one another.
3. The repulsive force and attractive force that exist between electric charges is called electrostatic force.
4. Electrostatic force on a charged object causes neutral objects to be attracted to it. Examples: bits of paper and hair.

Production of static electric charges

1. Static electric charges can be produced on a neutral object by rubbing it with a different material like a woollen or silk cloth.
2. When two different materials are rubbed, electron transfer occurs. One of the material receives electrons while the other loses electrons.
3. The material that receives electrons becomes negatively charged because it has more electrons than protons.
4. The material that loses electrons becomes positively charged because it has more protons than electrons.
5. An object is neutral if the number of positive charges (protons) and negative charges (electrons) is the same.

Detection of electric charges

1. An electroscope is used to detect small electric charges or static electric charges.
2. Charged materials can be detected by an electroscope.
3. Before it is used, the electroscope should be earthed by touching the metal disc with a finger. This is intended to neutralise the electroscope.
4. When a charged material is brought near the metal disc of the electroscope, its gold leaf will diverge.
5. When a material that is not charged (neutral) is brought near the metal disc of the electroscope, its gold leaf does not diverge.

Phenomena related to static electric charges in daily life

Friction between two materials produces electric charges. Because of this, electric charges can be produced anywhere:

Occurrence of lightning

• Clouds acquire electrical charges when water vapour in it rubs with air particles.
• Lightning can also occur when two groups of clouds of opposing charges come close to one another.
• Electric charges will jump from one group of clouds to another.
• Hence, lightning is produced.

Spark plug

• A spray of sparks is produced when a car engine is started.
• Electric charges 'jump' across spark space on the plug to produce sparks.
• These sparks cause fuel to burn to produce energy.

Nylon clothes

• A crackling sound is heard when we take off our nylon clothes on a dry day.
• This is because static electric charges are produced when the nylon clothes rub against our body.

Combing hair

• Dry hair will stand erect or will be attracted towards the comb on a dry day.
• This is because hair becomes charged when it rubs against the comb.

Electronic lighter

• Electric charges are produced when an electronic lighter is lit to produce sparks.
• The sparks will then ignite the gas.

Safety measures relating to static electric charges

Safety measures should be taken in certain situations relating to static electric charges: 

Lightning conductor

• The roofs of high buildings are usually installed with lightning conductors to protect these buildings from being struck by lightning.

Oil tanker

• An oil tanker becomes charged with static electricity when it moves because of friction with air particles.
• Furthermore, the rubber tyres prevent the charges from flowing to the Earth.
• Because of this, a metal chain is fixed to the bottom of the tanker to direct the charges to the Earth when the metal chain touches the ground.
• This is important as it prevents sparks from being produced that may cause a fire.

Aeroplane

• An aeroplane will acquire high electric charges when it rubs against the air as it flies.
• Aeroplane tyres are specially made to direct electric charges to the Earth when the plane lands.

Electricity

Sources of electrical energy

1. Electrical energy is energy produced when electric current flows.
2. A source of electrical energy is any device that produces electric charges or electric current.

Electric current

1. Moving electric charges (electrons) produce electric current.
2. Electric current is produced when electrons flow in a certain direction in a conductor.
3. Electric current is the rate of the flow of negative charges or electrons through a conductor.
4. The Van de Graaff generator is a device that can produce electric charges (electrostatic charges) of very high voltage on its dome.

Voltage

1. Voltage is electrical energy that is needed to enable electrons to flow from one point to another in a conductor.
2. Voltage produces force that pushes electrons through a circuit to produce electric current.

Resistance

1. The characteristic of a material that opposes the flow of electrons or electrical charges is called resistance.
2. A material with high resistance allows only a small current to pass through it.
3. Resistance in a conductor, for example a wire, depends on
   length of conductor
   The longer the conductor, the higher its resistance.
   diameter or thickness of conductor
   The bigger the diameter of the conductor, the lower its resistance.
   type of conductor
   Different types of conductor have different resistance.
   Copper and aluminium which are widely used as electric wires are a few metals that have low resistance.
4. Some conductors have high resistance to current that flows through them. This type of conductor is called a resistor.
5. The following laboratory activities are carried out to study the effects of length, thickness, and type of conductor on their resistance.

Direction of electron flow and current in an electric circuit

1. In a dry cell, current is produced when electrons flow from the negative terminal of the cell to the positive terminal through a wire.
2. However, the direction of current flow is the opposite of the direction of electron flow.
3. Electric current flows from the positive terminal to the negative terminal of a cell.

Measuring Electricity

Measuring electric current

1. Electric current that flows from a source of electrical energy can be measured with an ammeter.
2. The unit of measurement for current is ampere (A).
3. The ammeter is connected in series to a circuit when measuring current.
4. The positive terminal of the ammeter should be connected to the positive terminal of the

Measuring voltage

1. Voltage can be measured with a voltmeter.
2. The unit of measurement for voltage is volt (V).
3. The voltmeter is connected in parallel to a circuit when measuring voltage.
4. The positive terminal of the voltmeter should be connected to the positive terminal of the electric source in an electric circuit.

Measuring resistance

1. Resistance is measured in the unit of ohm.
2. The symbol of ohm is S2.
3. A resistor is a device that is used to reduce the electric current that flows in a circuit.
4. The bigger the ohm value in a resistor, the bigger is its resistance.

Relationship between Electric Current, Voltage and Resistance

Relationship between resistance and electric current

1. The quantity of electric current that flows through a circuit will change according to the resistance.
2. The bigger the resistance, the smaller the electric current that flows through a circuit.
3. If the resistance is small, the quantity of electric current that flows through a circuit will be big.

Relationship between voltage and electric current

1. The quantity of electric current that flows through a circuit will change according to the voltage.
2. The higher the voltage, the greater the electric current that flows through the circuit.
3. When the voltage of an electric source increases, the electric current that flow.

Relationship between voltage, electric current and resistance in ohm's law

1. The electric current that flows increases at the same rate as the rate of increase in voltage value.
2. The voltage quantity is directly proportional to the quantity of electric current.
3. The relationship between voltage, electric current and resistance is called Ohm's law.
4. R is constant for a fixed resistor. Therefore, the ratio of voltage to electric current, I, is always fixed. This fixed value is called resistance.
5. If a voltage (V) versus electric current (A) graph is drawn, a straight line that passes through the origin is obtained. The gradient of the graph represents the circuit resistance.
6. Ohm's law is used to solve problems related to values of voltage, electric current and resistance.
7. If any two values in the formula R =V/I are known, the third value can be determined.
8. The following steps are a guide to solving problems related to Ohm's law.

Parallel and Series Circuits

Symbols of electric circuit components

To make the drawing of an electric circuit easier, components of an electric circuit should be represented by certain symbols.

Electric circuit

1. An electric circuit is a path that allows electric current to flow through it.
2. The bulb will light up or the ammeter needle will deflect if an electric circuit is connected correctly.
3. There are two types of electric circuits, i.e.:
1. series circuit
2. parallel circuit

Series circuit

1. When circuit components like bulbs or resistors are connected from end to end or in a row, the circuit is called a series circuit.
2. The electric current flows on only one path from the positive terminal to the negative terminal of an electric source.
3. In a series circuit, if one part of the circuit is disconnected or a bulb is burnt, the circuit becomes incomplete and other bulbs will also be put out.

Parallel circuit

1. In a parallel circuit, electric components are arranged side by side and parallel to one another.
2. There is more than one path for the flow of electric current.
3. In a parallel circuit, if one bulb or resistor is spoilt or removed, electric current will still flow through another path. Other bulbs are still lit.
4. This type of circuit is used in buildings like homes and schools. Damage to one part of an electric circuit can be traced at once.

Electric Current, Voltage and Resistance in a Series Circuit

Flow of electric current in a series circuit

1. The ammeter gives the same reading even though it is connected at different positions. This shows that the current that flows in all the positions in a series circuit is the same.
2. If the current that flows through the ammeter X, Y dan Z are represented respectively by symbols I, /1 and 12, then the current values for I,11 and 12 are the same, i.e.:

Voltage in a series circuit

Voltage of cells in series

1. The more cells that are connected in series, the greater the current that flows. This is because more cells supply greater voltage or electrical energy to the circuit.
2. The total voltage is the same as the sum of the voltages of each cell.

Voltage of bulbs in series

1. The voltage across every circuit component like the bulb (or resistor) in a series circuit is the same.
2. If the voltage that is supplied by an electric source is represented by the symbol V and bulbs X and Y respectively use voltage value V1 and V2, then the relationship between V, V1 and V2 is

Resistance in a series circuit

1. If more bulbs are added in series, resistance in the circuit will increase causing the current that flows through the bulbs to decrease. Therefore, the bulbs will shine dimly.
2. If resistance of the bulbs is represented by R1 and R2, resistance (R) in a series circuit is the sum of the resistance in each bulb, i.e.:

Advantages and disadvantages of a series circuit

1. The advantages of a series circuit are as follows:
1. Current in all parts of the circuit is the same. This causes the bulbs to light up with the same brightness.
2. The current in the circuit increases if more cells are connected.
3. All circuit components are controlled by one switch.
2. The disadvantages of a series circuit are as follows:
1. There is only one path for the flow of electric current. If a bulb or lamp is burnt, other bulbs will not light up.
2. Cells in series do not last long.
3. If more bulbs are added, the resistance in the circuit increases causing the electric current that flows to decrease.

Electric Current, Voltage and Resistance in a Parallel Circuit low of electric current in a parallel circuit

1. In a parallel circuit, the quantity of current supplied by the electric source will be channelled to the branches according to their resistance value.
2. The quantity of current supplied by the electric source in a parallel circuit is same as the sum of the current that flows through each branch path.
3. If the current flowing through ammeter P, Q and R is represented by symbols I, II and 12 respectively, then the ampere value relationship of I, II and 12 is as follows.

Voltage in a parallel circuit

Voltage of cells in parallel

1. Voltage does not increase or decrease if cells of the same type are connected in parallel.
2. Compared to cells in series, cells in parallel are more lasting. The more cells there are in a parallel arrangement, the more lasting they are as electrical energy

Voltage of bulbs in parallel

1. The voltage across each bulb is the same as the voltage supplied by the electric source.
2. If the voltage recorded by the voltmeter at positions P, Q and R in Figure below are represented by symbols V, V1 and V2 respectively, then the voltage value relationship of V, V1 and V2 is as follows.

Resistance in a parallel circuit

If R is the total resistance and the resistance of the resistors in Figure below is represented by R1 and R2 respectively, then the relationship between R, R1 and R2 in the parallel circuit is

Advantages and disadvantages of a parallel circuit

1. The advantages of a parallel circuit are as follows:
1. If one of the bulbs is burnt, the other bulb(s) continues to shine.
2. Parallel cells last longer.
3. Each bulb receives the same voltage that is supplied by the electric source.
2. The disadvantages of a parallel circuit are as follows:
1. The voltage does not increase or decrease if cells of the same type are connected in parallel.
2. The electric current in the circuit is the same even though more cells are connected in parallel.