Energy and Electricity

Basic ideas… Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____. Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta. Resistance is anything that resists an electric current. It is measured in _____. Words: volts, amps, ohms, voltage, ammeter, voltmeter

Current in a series circuit If the current here is 2 amps… The current here will be… And the current here will be… In other words, the current in a series circuit is THE SAME at any point

Current in a parallel circuit A PARALLEL circuit is one where the current has a “choice of routes” Here comes the current… And the rest will go down here… Half of the current will go down here (assuming the bulbs are the same)…

Current in a parallel circuit If the current here is 6 amps The current here will be… And the current here will be…

Voltage in a series circuit V VV If the voltage across the battery is 6V… …and these bulbs are all identical… …what will the voltage across each bulb be? 2V

Voltage in a series circuit V V If the voltage across the battery is 6V… …what will the voltage across two bulbs be? 4V

Voltage in a parallel circuit If the voltage across the batteries is 4V… What is the voltage here? And here? VV 4V

Summary In a SERIES circuit: Current is THE SAME at any point Voltage SPLITS UP over each component In a PARALLEL circuit: Current SPLITS UP down each “strand” Voltage is THE SAME across each”strand”

An example question: V1V1 V2V2 6V 3A A1A1 A2A2 V3V3 A3A3

Advantages of parallel circuits… There are two main reasons why parallel circuits are used more commonly than series circuits: 1)Extra appliances (like bulbs) can be added without affecting the output of the others 2)If one appliance breaks it won’t affect the others either

Georg Simon Ohm Resistance Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. The resistance of a component can be calculated using Ohm’s Law: Resistance = Voltage (in V) (in  )Current (in A) V RI

An example question: V A 1)What is the resistance across this bulb? 2)Assuming all the bulbs are the same what is the total resistance in this circuit? Voltmeter reads 10V Ammeter reads 2A

More examples… 12V 3A 6V 4V 2A 1A 2V What is the resistance of these bulbs?

Two simple components: 2) Thermistor – resistance DECREASES when temperature INCREASES 1) Light dependant resistor – resistance DECREASES when light intensity INCREASES Resistance Amount of light Resistance Temperature

Current-voltage graphs I V I V I V 1. Resistor 3. Diode 2. Bulb Current increases in proportion to voltage As voltage increases the bulb gets hotter and resistance increases A diode only lets current go in one direction

DC and AC DC stands for “Direct Current” – the current only flows in one direction: AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz) 1/50 th s 240V V V Time T

Fuses Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____. Words – large, damage, safety, melt, live, circuit, fuse

Other safety devices… 1) Insulation and double insulation 2) Residual Current Circuit Breaker Insulating a wire prevents someone from touching the ____ wire. A device can also be double insulated – this is when the metal parts inside the device are insulated from the outer case. A double insulated device does not need an _______ wire but they still have _____. This circuit breaker detects any difference in current between the live and neutral connectors and switches off the current when needed. They can be easily _______. Words – earth, reset, live, fuses

The Cost of Electricity Electricity is measured in units called “kilowatt hours” (kWh). For example… A 3kW fire left on for 1 hour uses 3kWh of energy A 1kW toaster left on for 2 hours uses 2kWh A 0.5kW Vacuum Cleaner left on for 4 hours uses __kWh A 200W TV left on for 5 hours uses __kWh A 2kW kettle left on for 15 minutes uses __kWh

The Cost of Electricity To work out how much a device costs we do the following: Cost of electricity = Power (kW) x time (h) x cost per kWh (p) For example, if electricity costs 8baht per unit calculate the cost of the following… 1)A 2kW fire left on for 3 hours 2)A 0.2kW TV left on for 5 hours 3)A 0.1kW light bulb left on for 10 hours 4)A 0.5kW hoover left on for 1 hour 48B 8B 4B