S3 Physics – Exam revision

Electric current (I) is the flow of electric charge around a circuit and is measured in amperes (A) Voltage is a measure of the energy given to the charges in the circuit. Voltage is measured in volts (V)

Electrical symbols Cell A.C. Supply ?Low Voltage Supply? D.C. Supply Resistor Lamp Voltmeter Ammeter Switch ?connecting wire? Page 9 Physics study mate will help

Circuit symbols These symbols are used so that everyone worldwide can understand a circuit diagram when they see it.

Series circuits In a television series, you get several episodes, one after the other. A series circuit is similar. You get several components one after the other. If you follow the circuit diagram from one side of the cell to the other, you should pass through all the different components, one after the other, without any branches. In a series circuit, if a lamp breaks or a component is disconnected, the circuit is broken and all the components stop working. New Cell symbol

What will be the Ammeter readings on A 1 - 3 We measure electric current ( flow of electrons) with an ammeter (A). The circuit symbol for an ammeter is : A An ammeter must always be connected in series 8V d.c. A1 3 2 1 A4 A3 A2

What is actually going on in electric circuits? http://www.bbc.co.uk/learningzone/clips/an-introduction-to-electricity/10596.html Cell v battery v - - -

From the diagram above, what is the reading at: 1) Position 1: more than 0.1 A, 0.1 A or less than 0.1 A 2) Position 2: more than 0.1 A, 0.1 A or less than 0.1 A 3) Position 3: more than 0.1 A, 0.1 A or less than 0.1 A

Voltage Voltage is a measure of the energy given to the charges in the circuit. We measure voltage in volts (V). The circuit symbol for a voltmeter is : V A voltmeter must always be connected in parallel 8V d.c. v3 1 v2 v1 3 2

Resistance is measured in ohms – if a substance has a high resistance it will not allow electricity to flow through it

http://www.youtube.com/watch?v=BBa42qpKyfg Ohms law calculations Calculate the resistance of the resistor in the circuit. The current is 5A, the voltage across the resistor is 15V. A 5amp 15V

V I R Step 1: Choose the correct equation Step 2: Write down the equation. R = V ÷ I Step 3: Fill in the numbers for V and I. R = 15 ÷ 5 Step 4: work out your answer and do not forget to put in the correct units. R =3 Ω

V I R Copy and complete this table :- Voltage Current Resistance 0.2 A 60 12V 1000 230V 48 100 mA 1.5V 20 mA V I R

V I R Copy and complete this table :- Voltage Current Resistance (Ω) 60 12V 0.012 A 1000 230V 4.8 A 48 100 mA 2300 1.5V 20 mA 75 V I R

Which electrical quantity is measure in watts? Calculate the current in the hair dryer What size fuse should be fitted? Hair Dryer Super model 230 V 50 Hz 600 Watts

P = I V I = P V I = 600 = 2.6 Amp 230

Page 19 Success Guide Q 1 -5 Appliance Likely power rating Clock Upto 720 Watts Hair dryer 500 Watts Heater / fire 3,000 Watts Vacuum cleaner 1400 Watts Television 100 Watts (not a flat screen giant TV) Cooker 12000

The fuse 13 amp or 3 amp A safety device found in plugs & main fuse box If a larger current than normal flows then the fuse will melt This cuts off the electricity

The flex of my hair dryer only has two wires which terminal does not have a wire attached to it?

Type of wire Colour of wire Live Brown Earth Green and yellow Neutral Blue

The element of a heater has a current of 1 The element of a heater has a current of 1.25 amps and is plugged into UK mains voltage, what is it’s resistance? A - + Granny has a 1800 watt electric heater, she uses it 8 hours per day for one week – how many kilowatt-hours are used by Granny?

Series and parallel circuits What happens to the current flowing around these circuits? How would you describe the voltage in each of these circuits? How do we calculate the total resistance of each of these circuits?

Resistors in Parallel 15 Ω 10 Ω 10 Ω 30 Ω 10 Ω 5 Ω

From what we have learnt so far in Physics –Copy & Accurately complete this table Series Parallel Current Voltage Total Resistance

How did you do ? Out of ten? Series Parallel Current Voltage Is the same at all points The sum of currents in parallel branches is equal to the current drawn from the supply Voltage The sum of voltages across components in series is equal to the supply voltage The voltage across components in parallel is the same for each component Total Resistance R total = R1 + R2 = 1 + 1 Rtotal R1 R2

http://www.bbc.co.uk/bitesize/standard/physics/using_electricity/movement_from_electricity/revision/3/

On the following diagram of a basic DC electric motor label: the axle, the brushes, the commutator, the armature, the magnets, the current carrying loops. http://www.bbc.co.uk/bitesize/standard/physics/using_electricity/movement_from_electricity/revision/3/

Electric motor Commercial motors are different in several ways from the simple model discussed here. A commercial motor has carbon brushes for good electrical contact with the commutator and also so that when the brushes wear away, they can easily be replaced. Carbon brushes do not wear away as quickly as metal brushes A commercial motor has a multi-section commutator - two sections for each of several rotating coils wound in different planes. Although only one of these coils carries a current at any one time, having a lot of them makes the rotation far more smooth. A commercial motor uses field coils not a permanent magnet. These coils become magnetised when a current is passed through them. Field coils give a stronger, more easily shaped magnetic field than permanent magnets. cheaper / lighter

V I R Step 1: Choose the correct equation Step 2: Write down the equation. R = V ÷ I Step 3: Fill in the numbers for V and I. R = 15 ÷ 5 Step 4: work out your answer and do not forget to put in the correct units. R =3 Ω

We used an oscilloscope to view the difference between direct and alternating current Alternating current (a.c.) is when the current changes direction every fraction of a second. 50 times every second in UK. Direct current (d.c.) is when the current passes in one direction only. Batteries supply d.c.