AQA GCSE Physics Magnetism & Electromagnetism 4.7.. - 4.7.2.: Magnets & Electromagnets Name: Class: Date: Time: 55 minutes Marks: 55 marks Comments: Q to Q4 to be worked through with tutor. Q5 to Q7 to be worked through independently. Answers: http://www.harrowsmithtuition.co.uk/topictests/gcse/ aqa/4.7..-4.7.2..pdf
Figure shows two iron nails hanging from a bar magnet. The iron nails which were unmagnetised are now magnetised. Figure (a) Complete the sentence. Use a word from the box. forced induced permanent The iron nails have become magnets. ()
(b) Each of the three metal bars in Figure 2 is either a bar magnet or a piece of unmagnetised iron. The forces that act between the bars when different ends are placed close together are shown by the arrows. Figure 2 Which one of the metal bars is a piece of unmagnetised iron? Tick one box. Bar Bar 2 Bar 3 Give the reason for your answer. (2)
(c) A student investigated the strength of different fridge magnets by putting small sheets of paper between each magnet and the fridge door. The student measured the maximum number of sheets of paper that each magnet was able to hold in place. Why was it important that each small sheet of paper had the same thickness? () (d) Before starting the investigation the student wrote the following hypothesis: The bigger the area of a fridge magnet the stronger the magnet will be. The student s results are given in the table below. Fridge magnet Area of magnet in mm 2 Number of sheets of paper held A 40 20 B 0 6 C 250 6 D 340 8 E 350 4 Give one reason why the results from the investigation do not support the student s hypothesis. () (Total 5 marks)
2 A student is investigating the strength of electromagnets. Figure shows three electromagnets. The student hung a line of paper clips from each electromagnet. Figure Electromagnet A Electromagnet B Electromagnet C No more paper clips can be hung from the bottom of each line of paper clips. (a) (i) Complete the conclusion that the student should make from this investigation. Increasing the number of turns of wire wrapped around the nail will the strength of the electromagnet. () (ii) Which two pairs of electromagnets should be compared to make this conclusion? Pair : Electromagnets and Pair 2: Electromagnets and () (iii) Suggest two variables that the student should control in this investigation.. 2. (2)
(b) The cell in electromagnet A is swapped around to make the current flow in the opposite direction. This is shown in Figure 2. Figure 2 What is the maximum number of paper clips that can now be hung in a line from this electromagnet? Draw a ring around the correct answer. Give one reason for your answer. fewer than 4 4 more than 4 (2) (c) Electromagnet A is changed to have only 0 turns of wire wrapped around the nail. Suggest the maximum number of paper clips that could be hung in a line from the end of this electromagnet. Maximum number of paper clips = () (Total 7 marks)
3 The diagram below shows a door lock which can be opened from a flat inside a building. (a) Explain how the door is unlocked when the switch is closed. (4) (b) State two changes which would increase the strength of the electromagnet.. 2. (2) (c) Why is the spring needed in the lock? ()
(d) The connections to the coil were accidentally reversed. Would the lock still work? Explain your answer. (2) (Total 9 marks)
4 Circuit breakers help to make the electricity supply in homes safer. A circuit breaker is an automatic safety switch. It cuts off the current if it gets too big. Describe, in as much detail as you can, how this circuit breaker works. To gain full marks in this question you should write your ideas in good English. Put them into a sensible order and use the correct scientific words. (Total 6 marks)
5 (a) Diagram shows a magnetic closure box when open and shut. It is a box that stays shut, when it is closed, due to the force between two small magnets. These boxes are often used for jewellery. Diagram Diagram 2 shows the two magnets. The poles of the magnets are on the longer faces. Diagram 2 (i) (ii) Draw, on Diagram 2, the magnetic field pattern between the two facing poles. The magnets in the magnetic closure box must not have two North poles facing each other. Explain why. (2) (2)
(b) A student is investigating how the force of attraction between two bar magnets depends on their separation. She uses the apparatus shown in Diagram 3. Diagram 3 She uses the following procedure: ensures that the newtonmeter does not have a zero error holds one of the magnets puts sheets of paper on top of the magnet places the other magnet, with the newtonmeter magnetically attached, close to the first magnet pulls the magnets apart notes the reading on the newtonmeter as the magnets separate repeats with different numbers of sheets of paper between the magnets. The results are shown in the table. Number of sheets of paper between the magnets Newtonmeter reading as the magnets separate 0 20 30 40 50 60 70 80 20 3. 2.6 2..5.....
(i) Describe the pattern of her results. (2) (ii) No matter how many sheets of paper the student puts between the magnets, the force shown on the newtonmeter never reaches zero. Why? () (iii) The student is unable to experiment with fewer than 0 sheets of paper without glueing the magnet to the newtonmeter. Suggest why. (2) (iv) Suggest three improvements to the procedure that would allow the student to gain more accurate results. (3)
(v) The thickness of one sheet of paper is 0. mm. 6 (a) What is the separation of the magnets when the force required to separate them is 2. N? Separation of magnets = mm (3) (Total 5 marks) Electromagnets are often used at recycling centres to separate some types of metals from other materials. Give one reason why an electromagnet would be used rather than a permanent magnet. ()
(b) In this question you will gain marks for using good English, organising information clearly and using scientific words correctly. Some students want to build an electromagnet. The students have the equipment shown below. Describe how the students could build an electromagnet. Include in your answer how the students should vary and test the strength of their electromagnet. (6) (Total 7 marks)
7 Figure shows a magnet moving into a coil of wire. This movement causes a reading on the voltmeter. (a) Use the correct word from the box to complete the sentence. generated induced produced Moving the magnet into the coil of wire causes a reading on the voltmeter because a potential difference is across the ends of the wire. () (b) A student investigated how the number of turns on the coil of wire affects the maximum voltmeter reading. The student changed the number of turns on the coil of wire, then moved the magnet into the coil. The student recorded the maximum voltmeter reading. To obtain valid data, suggest two variables that the student should control in this investigation.. 2. (2)
(c) The student s results are shown in Figure 2. (i) One of the results is anomalous. Suggest a reason for the anomalous result. (ii) Draw a line of best fit on Figure 2. () () (d) A data-logger can automatically record and store data. It may have been better for the student to have used a data-logger in his investigation rather than a voltmeter. Suggest one reason why. () (Total 6 marks)
Mark schemes (a) induced (b) bar 2 (the same end) of bar attracts both ends of bar 2 or only two magnets can repel so cannot be bar or bar 3 (c) so the results for each magnet can be compared or so there is only one independent variable fair test is insufficient allow different thickness of paper would affect number of sheets each magnet could hold accept it is a control variable (d) because the magnet with the biggest area was not the strongest accept any correct reason that confirms the hypothesis is wrong eg smallest magnet holds more sheets than the largest [5]
2 (a) (i) increase (ii) (b) 4 (iii) A and B and B and C both required for the mark either order any two from: size of nail or nail material allow (same) nail current allow (same) cell allow p.d. same amount of electricity is insufficient (size of) paper clip length of wire accept type / thickness of wire 2 B picks up the same number as C, so this electromagnet would pick up the same number as A or direction of current does not affect the strength of the electromagnet allow it has got the same number of turns as A (c) 2 allow or 3 [7] 3 (a) current flows coil / core magnetised / electromagnet activated / energised / turned on attracts iron bar causing bolt to be pulled out each for mark 4
(b) (c) (d) more turns bigger current / e.m.f softer iron core any two for mark each to relock door / return iron bar / to lock door for mark iron bar would still be attracted / coil still magnetised so still works for mark each yes + wrong answer 0 marks yes + current still flows mark 2 yes + still magnetised / iron bar still attracted 2 marks 2 [9] 4 Quality of written communication: One mark for correct sequencing. bolt out --> plunger up --> switch off / circuit broken any five from high current flows electromagnet is stronger the iron bolt is pulled out the plastic plunger moves up the switch is lifted / open / off no current flowing accept circuit is broken to re-set the plunger must be pushed down 5 [6] 5 (a) (i) field pattern shows: some straight lines in the gap
direction N to S (ii) north poles repel (so) box will not close (b) (i) as paper increases (rapid) decrease in force needed force levels off (after 50 sheets) (ii) (iii) (iv) (v) the newtonmeter will show the weight of the top magnet (top) magnet and newtonmeter separate before magnets separate accept reverse argument (because) force between magnets is greater than force between magnet and hook of newtonmeter any three from: means of reading value of force at instant the magnets are pulled apart increase the pulling force gently or use a mechanical device to apply the pulling force clamp the bottom magnet use smaller sheets of paper fewer sheets of papers between readings (smaller intervals) ensure magnets remain vertical ensure ends of magnet completely overlap repeat the procedure several times for each number of sheets and take a mean make sure all sheets of paper are the same thickness 3 (mm) 30 0. ecf gains 2 marks 2. N corresponds to 30 sheets gains mark 3 3 [5]
6 (a) an electromagnet can be switched off accept a permanent magnet cannot be switched off or an electromagnet is stronger accept control the strength (b) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should apply a best-fit approach to the marking. Level 3 (5 6 marks): there is a description of how the electromagnet is made and there is a description of how the strength of the electromagnet can be varied and there is a description of how the strength of the electromagnet can be tested Level 2 (3 4 marks): there is a description of how the electromagnet is made and either there is a description of how the strength of the electromagnet can be varied or there is a description of how the electromagnet can be tested Level ( 2 marks): there is a basic description of how to make an electromagnet or there is a basic description of how the strength of the electromagnet can be varied or there is a basic description of how the electromagnet can be tested Level 0 (0 marks): No relevant / correct content
examples of the points made in the response Details of how to make an electromagnet wrap the wire around the nail connect the wire to the power supply (with connecting leads and croc clips) switch on the power supply accept a current should be sent along the wire Details of how to vary the strength of the electromagnet change the number of turns (on the coil) change the current (through the coil) change the separation of the turns allow change the potential difference (across the coil) accept wrap the coil more tightly Details of how to test the electromagnet suspend paperclips from the electromagnet the more paperclips suspended, the stronger the electromagnet is clamp the electromagnet at different distances from the paperclip(s) the further the distance from which paperclips can be attracted the stronger the electromagnet is test before and after making alterations to change the strength compare the results from before and after making alterations use de-magnetised paper clips accept count the number of paperclips with different current or p.d. or no. of turns or core and see if the number changes/increases 6 [7] 7 (a) induced (b) any two from: use the same (strength) magnet same size magnet is insufficient the speed that the magnet is moved accept movement of the magnet the area of the turns same type / length of wire is insufficient the magnetic pole being moved towards the coil (of wire). use the same voltmeter is insufficient 2
(c) (i) voltmeter misread or number of turns miscounted result misread is insufficient human error is insufficient allow the magnet was moved at a (slightly) different speed (into the coil) than for the other readings allow spacing between the turns had changed (ii) line of best fit passing through all points except (00, 0.034) line does not need to go back to origin (d) any one from: can re-check data / readings. accept can go back to data can take more readings (in a given time) can store data is insufficient easier to identify maximum value. automatically records data is insufficient accept is more accurate accept eliminates human error [6]
Examiner reports 2 (a) (i) The vast majority of students correctly completed the conclusion. (ii) A third of the students correctly identified the two pairs of electromagnets. (iii) Most students were able to identify at least one of the variables that needed to be kept the same. However, some quoted the dependent variables, others gave vague responses of power / electricity rather than p.d. or current. (b) (c) Half of the students scored both marks for identifying the number of paperclips and a correct reason. Almost every student scored the mark. 4 Foundation Tier Most candidates gained some credit on this question, with the better candidates producing very good descriptions. Some chose simply to describe what they could see in the two diagrams rather than describe the sequence of events that would cause the circuit to break. Incorrect ideas that were frequently seen were that, the coils heat up, the springs pass the current or the button must be pressed to switch off the electricity. Very few candidates understood that as a consequence of an increased current the electromagnetic attraction increases and attracts the iron bolt. Higher Tier Most candidates gained credit on this question, with the better candidates producing very good, detailed descriptions. Some weaker candidates chose simply to describe what they could see in the two diagrams rather than describe the sequence of events that would cause the circuit to break. There were, however, only a few candidates who understood that as a consequence of an increased current, the electromagnetic attraction increases and attracts the iron bolt. 6 Foundation (a) Many students thought that an electromagnet could somehow be adjusted to pick up a variety of specific metals. It was also not uncommon to see students stating that the electromagnet could separate metals, failing to realise that they were comparing the electromagnet with a permanent magnet, which would also be able to separate metals. (b) The vast majority of students attempted this question, but many struggled to describe how to put an electromagnet together, and in particular it was not uncommon for students to connect the ends of the nail to the power supply. There was also a small minority of students who tried to express the intention to strip the ends of the insulating wire and attach crocodile clips to this, but actually described stripping the entire insulating wire. A few students thought that the insulating wire was to keep their electromagnet thermally insulated. Of those who did manage to describe the construction of an electromagnet well, most could describe a test to see if their electromagnet was working, but many struggled to increase the strength of the electromagnet, with comments indicating that they should turn up the power on the power supply, rather than increasing p.d., current or number of turns on the coil. Just less than half of students accessed Levels 2 or 3.
Higher 7 (a) (b) (a) (b) Nearly four fifths of students answered this question correctly. The most common reason for not answering correctly was for stating that the electromagnet could separate metals, failing to realise that they were comparing the electromagnet with a permanent magnet, which would also be able to separate metals. Many students struggled to describe how to construct an electromagnet; in particular it was not uncommon to see students connecting the ends of the nail to the power supply, or failing to make clear whether the insulating wire or the iron nail was connected to the power supply. Most students who managed to do this correctly went on to describe a test for the strength of the electromagnet, although a significant number of students merely tested whether the electromagnet could pick up paperclips, and did not count how many. A number of students were confused between changing the strength of the electromagnet and testing the strength of it; it was not uncommon to see students stating that an electromagnet could be tested by adding more turns to the coil on the nail. About a third of students gave Level 3 responses to this question. A common reason for a student reaching Level 2 but not getting into Level 3 was that they talked about increasing the power from the power supply, rather than increasing the current or potential difference. Just under a quarter of students gave Level 2 responses. Only just over one third of the students scored this mark. A small minority of the students scored both marks but just over half of the students scored one mark. Many students suggested changes in material or thickness of the wire. It was also common to see students controlling the size of the magnet, but not the strength of it. A fair proportion of students answers suggested that using the same voltmeter should be a control variable. Some students did not appreciate that the number of turns on the coil was the independent variable, despite this being clearly stated in the question. (c) (i) Nearly one third of the students scored this mark. Many students did not give enough detail in their answer, referring to human error but not stating what that human error was. A number of students did not read the question properly and either gave a definition of the term anomaly or indicated which the anomalous point was. (ii) This question was generally answered well, with most of the students drawing the line well. A larger proportion of students did not attempt this question compared to questions which involved ticking a box or writing on a line, suggesting that these students did not read the question. (d) Just under two thirds of the students scored the mark, with the majority of the correct answers mentioning the improved accuracy of using a data-logger in this situation. A fair number of students suggested that a data logger would eliminate anomalies, failing to realise that anomalies in this investigation could be caused by a change in speed of the movement of the magnet as well as human errors in mis-reading the voltmeter or miscounting the coils.