Presentation on theme: "Boardworks GCSE Separate Sciences 2009 Transformers"— Presentation transcript:
1 Boardworks GCSE Separate Sciences 2009 Transformers
2 Boardworks GCSE Separate Sciences 2009 Transformers
3 Boardworks GCSE Separate Sciences 2009 Transformers Current and magnetismBoardworks GCSE Separate Sciences 2009TransformersEvery electric current produces a magnetic field. The shape and strength of the magnetic field depends on the shape of the wire carrying the current. A single straight wire carrying a direct current is surrounded by a circular magnetic field:Every point on an infinite wire is equivalent to every other, so the magnetic field must be the same at every point – it is made up of concentric circles.A much stronger magnetic field can be made by twisting a wire into a tight coil, or solenoid. This creates a magnetic field like that of a bar magnet.
4 Boardworks GCSE Separate Sciences 2009 Transformers Field around a wireBoardworks GCSE Separate Sciences 2009TransformersThe direction of the magnetic field around a straight wire can be worked out by using the right hand grip rule.–Grip a wire so that your thumb points in the direction of the conventional current (from the positive to the negative terminal of a battery).+Your fingers will curl around the wire in the direction of the magnetic field (from north to south pole).
5 Field around a solenoid Boardworks GCSE Separate Sciences 2009TransformersThe right hand grip rule can also be used to find the orientation of the magnetic field around a solenoid:N–Grip the solenoid so that your fingers follow the direction of the conventional current.+Your thumb will now point towards the north pole of the electromagnet created by the solenoid.STeacher notesStudents should be made aware that the direction of a magnetic field is usually taken as being N–S rather than S–N, but in this rule the thumb is seen as pointing towards the north pole.The electromagnet can be made stronger by increasing the number of coils, or by adding an iron core.
6 Inducing current in a coil Boardworks GCSE Separate Sciences 2009Transformers
8 Electricity and magnetism Boardworks GCSE Separate Sciences 2009Transformers
9 Boardworks GCSE Separate Sciences 2009 Transformers
10 Linking circuits with magnetism Boardworks GCSE Separate Sciences 2009Transformers
11 Linking circuits with magnetism – results Boardworks GCSE Separate Sciences 2009TransformersIn the experiment, a current was induced in the second circuit when the first circuit was switching on or off. In order for power to be transferred continuously between two circuits, the current in the first circuit must be changing continuously.This can be achieved by using an alternating current.In order for as much power to be transferred as possible, the two circuits must be as closely magnetically linked as possible.This can be achieved by winding the two circuits into tight coils around an iron core. This is a transformer.
12 Primary side – how it works Boardworks GCSE Separate Sciences 2009TransformersA transformer links two circuits together. To understand how it works, it is important to look at each side separately.The primary side is simply an electromagnet. By passing an electric current through a coil of wire, we make a magnetic field, just like the field around a bar magnet.Direct current makes one end of the iron north, and the other end south.–NS+
13 Secondary side – how it works Boardworks GCSE Separate Sciences 2009TransformersThe secondary side is not connected directly to any power supply. It is just a piece of iron with some wire wrapped around it.The secondary side works using electromagnetic induction. To make a current flow, a magnetic field needs to be changing perpendicular to the coil.When there is an alternating current in the primary side, the direction of the magnetic field around the transformer alternates. This induces a second alternating current in the secondary side.
14 How a transformer works – summary Boardworks GCSE Separate Sciences 2009Transformers
15 Boardworks GCSE Separate Sciences 2009 Transformers Parts of a transformerBoardworks GCSE Separate Sciences 2009Transformers
16 Boardworks GCSE Separate Sciences 2009 Transformers
17 Properties of transformers Boardworks GCSE Separate Sciences 2009TransformersTransformers transfer power between circuits.The design of a transformer determines the characteristics of the electricity flowing in its secondary circuit. The frequency of the alternating current in the secondary circuit will always match the primary circuit, but what about current and voltage?The voltage in each circuit is related to the number of coils on each side of a transformer by the following equation:primary voltageprimary turns=secondary voltagesecondary turnsVpNp=VsNs
18 Boardworks GCSE Separate Sciences 2009 Transformers Step-up transformersBoardworks GCSE Separate Sciences 2009TransformersA step-up transformer is used to increase voltage. It has more turns on its secondary side than on its primary side.But the power in the secondary circuit cannot be greater than the power in the primary circuit, or the transformer would be more than 100% efficient!What is the relationship between power, voltage and current?P = V × IA step-up transformer increases voltage, but reduces current.
19 Step-up transformer calculations Boardworks GCSE Separate Sciences 2009TransformersA transformer has 100 turns on its primary coil. It has an input voltage of 35 V and an output voltage of 175 V.How many turns are on the secondary coil?VpNpVs=Ns=× NpVsNsVpVsNs175Ns=× 100=35VpNpNsVs= turns=NpVp
22 Step-down transformers calculations Boardworks GCSE Separate Sciences 2009TransformersA transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920 V.What is the output voltage?VpNp=VsNsVsNs=VpNpNsVs=× VpNp50Vs=× 920= 230 V200
23 Isolating transformers Boardworks GCSE Separate Sciences 2009TransformersAn isolating transformer has the same number of coils on its primary and secondary sides.A transformer has 100 turns on the primary side, and 100 turns on the secondary side. If the primary voltage is 230 V, what is the secondary voltage?VpNpNp = Ns== 1VsNsNp= 1Vs=Vp=230 VNs
25 Transformers around the home Boardworks GCSE Separate Sciences 2009Transformers
26 Step-down transformer uses Boardworks GCSE Separate Sciences 2009Transformers
27 Transformers around the home Boardworks GCSE Separate Sciences 2009TransformersHow many transformers can you find in this house?Teacher notesThis illustration contains several examples of transformers in use, for example:Several electrical items have large plugs, which contain transformers, including the digital phone and printer.Other items have normal plugs, but run on small voltages and must contain internal transformers, such as the television and games console.The laptop is connected to the mains by a cable that incorporates a box transformer.In the bathroom, an electrical shaver is visible. The shaver socket contains an isolating transformer.There are also a few red herrings in the picture, such as the kettle, toaster and electric heater, which all run on mains voltage.
28 Boardworks GCSE Separate Sciences 2009 Transformers
29 What is the National Grid? Boardworks GCSE Separate Sciences 2009TransformersThe National Grid is a network of power lines designed to carry mains electricity around the country, from the power stations where it is generated to the homes and factories where it is used.Transformers are an important part of the National Grid, because electricity must be transported at a much higher voltage than it is generated at or used at in homes.
30 Boardworks GCSE Separate Sciences 2009 Transformers Power loss in cablesBoardworks GCSE Separate Sciences 2009TransformersWhen electrical energy is carried in wires, a current must flow.There is a power loss in cables which is related to the amount of current flowing:power loss = current2 × resistanceP = I2 × RPower is measured in watts (W).Current is measured in amps (A).Resistance is measured in ohms (Ω).
31 Power loss in cables – example Boardworks GCSE Separate Sciences 2009Transformers
32 Boardworks GCSE Separate Sciences 2009 Transformers Transformer powerBoardworks GCSE Separate Sciences 2009TransformersA step-up transformer may increase voltage but it cannot create energy!primarysecondaryIn a perfect transformer the power in is equal to the power out. As power = V × I, if voltage goes up, then current must go down.VsVpIsIppower in = power outPp = PsVp × Ip = Vs × Is
33 Transformer power example Boardworks GCSE Separate Sciences 2009TransformersA transformer has a primary voltage of 1000 V and a primary current of 0.5 A.If the secondary circuit has a current of 0.01A flowing, what is the secondary voltage?primarysecondaryVp × Ip = Vs × IsVsVpIpVs=Vp ×IsIsIp0.5=1000 ×= V0.01
36 Boardworks GCSE Separate Sciences 2009 Transformers The National GridBoardworks GCSE Separate Sciences 2009Transformers
37 Boardworks GCSE Separate Sciences 2009 Transformers
38 Boardworks GCSE Separate Sciences 2009 Transformers GlossaryBoardworks GCSE Separate Sciences 2009TransformersGlossaryalternating current – A flow of electricity that switches direction periodically, such as that supplied by the National Grid.direct current – A flow of electricity in a fixed direction, such as that supplied by a battery.dynamo effect – Another term for electromagnetic induction.electromagnetic induction – The effect whereby a current is induced in a wire by a changing magnetic field.generator – A device that uses the dynamo effect, or electromagnetic induction, to convert mechanical energy into electrical energy.isolating transformer – A transformer designed to isolate a circuit from the mains for safety reasons, without altering the supplied voltage.magnetic field – The area around a magnet where its influence can be felt.mains electricity – The domestic electrical power supply with a voltage of 230 V.National Grid – The network of high-voltage power lines that carries electricity from power stations across the country.power – The rate of electrical energy transfer in a circuit, which is equal to the product of current and voltage.power station – A facility where electrical power is generated.primary coil – The coil around the primary side of a transformer.primary side – The part of a transformer that uses an alternating power supply to produce an alternating magnetic field.right hand grip rule – A rule that uses the fingers and thumb of the right hand to predict the direction of the magnetic field around a current.secondary coil – The coil around the secondary side of a transformer.secondary side – The output side of a transformer, where the changing magnetic field in the transformer’s core induces an alternating current.step-down transformer – A transformer that reduces voltage, with a smaller number of turns on its secondary coil.step-up transformer – A transformer that increases voltage, with a larger number of turns on its secondary coil.transformer – A device that transfers power between two unconnected electrical circuits.
39 Boardworks GCSE Separate Sciences 2009 Transformers AnagramsBoardworks GCSE Separate Sciences 2009Transformers
40 Boardworks GCSE Separate Sciences 2009 Transformers Multiple-choice quizBoardworks GCSE Separate Sciences 2009TransformersTeacher notesThis multiple-choice quiz could be used as a plenary activity to assess students’ understanding of transformers. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by completion on the IWB.