Electricity

Starter: What is current? What is it measured in? What is it measured by?

Which is the series and parallel circuit? (see board)

Current in series and parallel circuits…

•Current in a series circuit… …..is the same, no matter where in the circuit it is measured.

•Current in a parallel circuit… …..add up to equal the current from the power supply.

Question

•Which of the ammeter positions in the parallel circuit show us the current value of the power supply??

Ans: A1 and A3A1

A2

A3

A4

A5

Voltage

•Voltage is a measure of how good a battery is at pushing electrons around a circuit or how much energy the current has. Increasing the voltage increases the current.

•Voltage can also be called the potential difference.

•The symbol for voltage is V. It is measured in a unit called volts.

•Voltage is measured with a voltmeter.

•A voltmeter is connected across a component. The positive side of the terminal must lead back to the positive terminal of the power supply.

Voltage in series and parallel circuits

•In series the voltage is shared between the components.

•In parallel the voltage in each branch equals that of the power supply.

Resistance

•Resistors are components that restrict the flow of electrons (current).

•Resistance is the voltage lost by each ampere of current.

•The symbol for resistance is R and the unit is Ohms, Ω.

•Resistance is calculated from the values of current and voltage in a circuit.

•Resistance in a circuit causes electrical energy to be transferred to heat energy.

Ohm’s Law

•Complete practical

Starter…

• In a series circuit the current is the _________ everywhere around the circuit.

• In a parallel circuit the current is ___________ between the branches of the circuit.

• In a series circuit the voltage is ____________ between the __________.

• In a parallel circuit the voltage converted by each component ____________ the voltage supplied by the ____________.

Resistance

Resistance is the property of a substance that restricts the flow of electrons through it. In seriesThe total resistance will always be higher than any single resistor Rtotal = R1 + R2 + R3

The total amount of current supplied to the circuit decreases as more resistors are added in series

In parallel

The total resistance will always be lower than any single resistor

The total amount of current supplied to the circuit increases as more resistors are added in parallel

Ohm’s Law Experiment

Investigating the relationship between current, voltage and resistance…Follow instructions on handoutRecord current and voltage readingsDraw circuit diagram into your bookDraw graph showing relationship between current,

voltage and resistance

Ohm’s Law

9.09.11 Do now:

• In a series circuit the voltage is ____________ between the __________.

• In a parallel circuit the voltage converted by each component ____________ the voltage supplied by the ____________.

• In a series circuit the current is the _________ everywhere around the circuit.

• In a parallel circuit the current is ___________ between the branches of the circuit.

POWER

•In an electrical circuit, power (P) refers to the rate at which electrical energy is:Used by a component (e.g. lamp or

resistor), orSupplied by a battery or power pack.

•Unit for power is the watt (W). •1 watt means that 1 joule (J) of electrical

Energy (E) is used per second.

Earthing

Earth wires

• Many electrical appliances have metal cases, including cookers, washing machines and refrigerators. The earth wire creates a safe route for the current to flow through, if the live wire touches the casing.

• You will get an electric shock if the live wire inside an appliance, such as a cooker, comes loose and touches the metal casing.

• However, the earth terminal is connected to the metal casing, so the current goes through the earth wire instead of causing an electric shock.

Equations you need to know how to use:

•V = IR•P = IV•P = E t •RT = R1 + R2…..

Try these:1. A multibox is plugged into the mains and is

being supplied with 240 Volts of electrical energy.

A toaster drawing 12 Amps of current is plugged into the multibox and switched on. How much electrical power is the toaster using?

_______________W

2. The following information is printed on the front of a multibox: Maximum total load: 15A 3000W a) How much electrical power can this multi-box safely use?__________ b) How much electrical current can this multi-box safely use?__________ 3. a) The multi-box is plugged into the mains and is being supplied with 240

Volts of electrical energy. A toaster drawing 7 Amps of current is plugged into the multi-box and

switched on. How much electrical power is the toaster using? _______________W b) Use the answer above to explain whether or not the toaster is overloading

the multi-box c) The toaster is used for 60 seconds before being switched off. How much

electrical energy does the toaster use during this time? ___________ (Unit) _____

•When resistors are added into a series circuit, resistance __________(increases/decreases)?

•When resistors are added into a parallel circuit, resistance __________(increases/decreases)?

• If I have a phone charger (R1= 3Ω), a toaster (R2= 5Ω) and a kettle (R3= 10Ω) in a series circuit, what would the total resistance be?