08 Static Electricity 62 minutes 62 marks Q1.(a) A student uses some everyday items to investigate static electricity. 1 A strip of plastic is cut from a plastic carrier bag 2 The plastic strip is rubbed with a cloth 3 The plastic strip is hung over a wooden rod (i) Draw a ring around the correct answer in the box to complete each sentence. Rubbing the plastic strip with a cloth causes the strip to become negatively charged. electr ons This happens neutro move from the cloth onto the
Transcript
08 Static Electricity
62 minutes
62 marks
Q1.(a) A student uses some everyday items to investigate static electricity.
1 A strip of plastic is cut from a plastic carrier bag
2 The plastic strip is rubbed with a cloth
3 The plastic strip is hung over a wooden rod
(i) Draw a ring around the correct answer in the box to complete each sentence.
Rubbing the plastic strip with a cloth causes the strip to become negatively charged.
electrons
This happens because neutrons move from the cloth onto the plastic strip.
protons
a negative
The cloth is left with a positive charge.
zero
(2)
(ii) When the plastic strip is hung over the wooden rod, the two halves of the strip move equally away from each other.
What two conclusions should the student make about the forces acting on the two halves of the plastic strip?
(b) Electrical charges move more easily through some materials than through other materials.
Through which one of the following materials would an electrical charge move most easily?
Draw a ring around your answer.
aluminium glass rubber
(1)(Total 5 marks)
Q2.(a) The diagram shows a negatively charged plastic rod held near to a thin stream of water. The water is attracted towards the rod.
Which one of the following statements explains what is happening to the charge in the water?
Tick ( ) one box.
The positive and the negative charges in the water are attracted to the rod.
The positive and the negative charges in the water are repelled by the rod.
The negative charge in the water is repelled by the rod and the positive charge is attracted to the rod.
The negative charge in the water is attracted to the rod and the positive charge is repelled by the rod.
(1)
(b) A company that produces bottles of mouthwash found a problem with the automatic filling system.
As the bottles go towards the filler, the bottles move around on the conveyor belt and become electrostatically charged. This causes the stream of mouthwash to move sideways, missing the open top of the bottle.
The company came up with an answer to the problem. Before the bottles reach the dfiller, the bottles pass through a stream of ionised air. The ions in the air neutralise the charge on the bottles.
(i) Explain why the plastic bottles became charged.
Q3. (a) Fine powders poured through a pipe can become charged. The diagram shows the apparatus used by a student to investigate this effect.
The student poured 75 cm3 of polystyrene beads down the pipe. The beads fell into a metal can and the charge on them was measured directly using a coulombmeter.
The student repeated this twice more, but each time used 75 cm3 of beads of a different size.
(i) When they fell through the pipe, the polystyrene beads became negatively charged.
(d) The table gives the minimum ignition energy (MIE) value for a number of fine powders.The MIE is the minimum amount of energy required to cause a fine powder to ignite.
Type of powder MIE in millijoules
Coal dust 60.00
Aluminium powder 10.00
Cornstarch dust 0.30
Iron powder 0.12
The MIE values for different substances are all measured in the same way and under the same conditions of pressure and temperature.
(b) A student put the charged polythene rod on to a balance. The rod was separated from the metal pan of the balance by a thin block of insulating material.The student then held a second charged polythene rod above, but not touching, the first rod. The reading on the balance increased.
(i) Explain why the reading on the balance increases.
Q5. (a) The diagram shows a negatively charged plastic rod held close to a thin stream of water. The water is attracted towards the rod.
Which one of the following statements explains what is happening to the charge in the water?
Tick ( ) one box.
The positive and the negative charges in the water are attractedto the rod.
The positive and the negative charges in the water are repelledby the rod.
The negative charge in the water is repelled by the rod and thepositive charge is attracted.
The negative charge in the water is attracted by the rod and thepositive charge is repelled.
(1)
(b) A company that produces bottles of mouthwash found a problem with the automatic filling system.
As the bottles go towards the filler, they move around on the conveyer belt and become electrostatically charged. This causes the stream of mouthwash to move sideways, missing the open top of the bottle.
The company came up with a solution to the problem. Before the bottles reach the filler, they pass through a stream of ionised air. The ions in the air neutralise the charge on the bottles.
(i) Explain why the plastic bottles become charged.
Q8. (a) The diagram shows a student touching the metal dome of a Van de Graaff generator.When the generator is switched on, the metal dome becomes negatively charged.
Explain why the student’s hair stands on end when the generator is switched on.
(b) When the potential difference between the student and a nearby earthed metal dome reached 15 kV, a spark jumped between the student and the earthed dome. The spark transformed 30 mJ of energy into heat, light and sound. (1 mJ = 0.001 J)
Use the equation in the box to calculate the charge carried by the spark.
energy transformed = potential difference × charge
(b) Scientists were asked to find out whether the build-up of charge on the driver depends on the type of material used to make the driver’s clothes. The results of the investigation are given in the table.
Material Humidity Temperature in C Charge on the driverin millicoulombs
Nylon 48% 18 3.0 to 3.2
Wool 48% 18 2.4 to 2.5
Cotton 48% 18 1.4 to 1.7
Humidity is a measure of how much water vapour the air can hold.
(i) Why was it important that the scientists controlled the humidity?
(iii) The negatively charged comb is placed close to a charged plastic ruler. The comb and the ruler attract each other.
Complete the following sentence by drawing a ring around the correct line in the box.
The ruler is
negatively charged
positively charged
uncharged
(1)
(b) Electrostatic charge can damage computer chips. People working with computer chips may wear a special bracelet, with a wire joining the bracelet to earth (the earth wire). Any negative charge on the person will flow through the wire to earth.
(i) Which one of the following materials should the bracelet be made from?
(ii) Which one of the following words is used to describe the rate of flow of charge through a wire?
Draw a ring around your answer.
current resistance voltage(1)
(Total 7 marks)
M1.(a) (i) electrons1
a positive1
(ii) (forces are) equalaccept (forces are)the sameforces are balanced is insufficient
1
(forces act in) opposite directionsaccept (forces) repelboth sides have the same charge is insufficient
1
(b) aluminium1
[5]
M2.(a) 3rd box The negative charge in the water is repelled by the rod and the positive charge is attracted to the rod.
1
(b) (i) friction between bottles and conveyor belt / (plastic) guidesaccept bottles rub against conveyor belt / (plastic) guides
1
charge transfers between bottles and conveyor belt / (plastic) guidesaccept specific reference eg electrons move onto / off the bottles reference to positive electrons / protons negates this mark
1
(ii) (the atom) loses or gains one (or more) electrons1
(iii) charge will not (easily) flow off the conveyor belt / bottlesaccept the conveyor belt / bottles is an insulator / not a conductor accept conveyor belt is rubber
1[5]
M3. (a) (i) friction between the beads and pipeaccept beads rub against the pipe
1
(cause) electrons to transferaccept electrons are lost/gaineddo not accept negatively charged atoms for electrons3rd mark point only scores if 2nd mark scores
1
from the pipedo not accept from the (negatively) charged pipe
orto the beadsdo not accept to the (positively) charged beadsaccept negative charge transfer to the beads for 1 mark provided 2nd or 3rd marking point not awardedmention of positive charge transfer negates last 2 marking points
1
(ii) volume of beadsaccept (75)cm3
orlength of pipe
accept use the same pipe
orspeed the beads are poured
poured the same way is insufficientorangle of pipe
1
(b) (i) the larger the beads the less chargedo not accept inversely proportionalnegative correlation is insufficient
1
(ii) (total) charge decreaseresults would be lower/smaller would be insufficient
1
beads in contact with pipe (walls) for less timeaccept less contact (between beads and pipe)accept beads in pipe for less time
orsmaller surface area (to rub against)
accept less pipe to rub againstless friction is insufficient
1
(c) (i) (pumping very) fine powdersreason only scores if (very) fine powders given
greater charge (build up)accept more static (electricity)accept an answer that correctly relates back to the experimental data
orhigher pd/voltageorgreater energyaccept larger surface area to volume (ratio)
1
(ii) idea of earthing (the pipe)accept use metal pipesdo not accept use larger particles
1
(d) to compare (the relative risks)fair test is insufficientyou can only have oneindependent variable is insufficient
ordifferent conditions change the MIE value
accept different conditions change the resultsdo not accept avoid bias
1[10]
M4. (a) electrons transfer / removeddo not accept negatively charged atoms for electronsthis only scores if first mark given
1
to the rod / from the cloththis does not score if there is reference to any original charge on cloth or rod‘it’ refers to the rodaccept negative charge transfer to rod / removed from cloth for 1marktransfer of positive charge / positive electrons scores zero
1
(b) (i) rods / charges repel1
creating downward / extra force (on the balance)accept pushing (bottom) rod downwardsdo not accept increasing the weight / masscharges attracting scores zero
1
(ii) the (repulsion) force increases as the distance between the chargesdecreases
accept there is a negative correlation between (repulsion) force and distance between chargesor(repulsion) force and distance between charges are inversely proportionalfor both marksexamples of 1 mark answersforce increases as distance decreasesforce and distance are inversely proportionalnegative correlation between force and distancerepels more as distance decreasesif given in terms of attracting or attraction force this mark does not score
2[6]
M5. (a) 3rd box
The negative charge in the water is repelled by the rod and
the positive charge is attracted.1
(b) (i) friction between bottles and conveyor belt / (plastic) guidesaccept bottles rub against conveyor belt / (plastic) guides
1
charge transfers between bottles and conveyor belt / (plastic) guidesaccept specific referenceeg electrons move onto / off the bottlesreference to positive electrons / protons negates this mark
1
(ii) an atom that has lost / gained electron(s)do not accept a charged particle
1
(iii) charge will not (easily) flow off the conveyor beltaccept the conveyor belt / bottle is an insulator / not a conductoraccept conveyor belt is rubber
1[5]
M6. (a) fleece rubs against shirtit refers to the fleece
1orfriction (between fleece and shirt)
(causing) electrons to transfer from one to the otheraccept a specific direction of transferdo not accept charge for electronspositive electrons negates this markmovement of protons negates this mark
1
(b) Electrical charges move easily through metals.1
An electric current is a flow of electrical charge.1
(c) (i) copperreason only scores if copper chosen
1
(good electrical) conductor
accept it is a metalany mention of heat conduction negates this mark
1
(ii) lower than1
(iii) accept any sensible suggestion,eg:
• too many variables (to control)
• lightning strikes / storms are random / unpredictable
• do not know which building will be struck
• do not know when a building will be struck
• do not know when lightning will happen
• (very) difficult to create same conditions in a laboratory
• lightning storms are not the sameit is not safe is insufficientdo not accept lightning does not strike the same place twice
1[8]
M7. (a) repel1
opposite1
attract1
correct order only
(b) refuelling an aircraftreason cannot score if refuelling aircraft is not chosen
1
a spark may cause an explosion / fire / ignite the fuelaccept the static for a sparkaccept named fuelthere must be a consequence of having a sparkdo not accept answers in terms of people getting a shock or electrocuted
1[5]
M8. (a) each hair gains the same (type of) chargeor(each) hair is negatively chargeddo not accept hair becomes positively charged
or(each) hair gains electrons1
similar charges repelaccept positive charges repelproviding first marking point is in terms of positive charge
ornegative charges repelorelectrons repel
1
(b) 0.000002accept correct substitution and transformation for 1 mark
or 2 × 10-6
ie 30 / 15 or .03 / 15000 or 30 / 15000 or .03 / 15or 2 μ C
answers 2 and 0.002 gain 1 mark2
(c) currentdo not accept amp / amperes
1[5]
M9. (a) clothing and seat rub togetheraccept friction between clothing and seat
1
electrons transfer from seat to driver
or
electrons transfer from driver to seataccept electrons transfer on its own if first mark scoresan answer in terms of rubbing, between clothing and seat andcharge transfer without mention of electrons gains 1 markan answer in terms of friction / rubbing and electron transferwithout mention of clothing and seat gains 1 mark
1
(b) (i) how wet the air is affects charge (build up)accept humidity affects charge
or
damp air is a better conductor
or
damp air has a lower resistancedo not accept fair test or as a control unless explained
1
(ii) No – it was only the lowest under these conditionsaccept answer in terms of changing the conditions may change the results
or
No – there are lots of other materials that were not tested
or
Yes – the highest value for cotton is smaller than the lowest value forthe other materials
do not accept results show that it is always less / smallest1
[4]
M10. (a) (i) electrons1
jumper1
(ii) positiveaccept protonsaccept +
1
(iii) positively chargedaccept any clear way of indicating the answer
1
(b) (i) copper1
it is an (electrical) conductoronly accept if copper is identifieddo not accept it conducts heat
accept it conducts heat and electricityaccept copper is the best conductoraccept correct description of conduction
1
(ii) current1
[7]
E1.(a) (i) Just over half of students gained both marks.
(ii) Many students tended to answer the question in terms of static charge rather than describing the forces as asked. About half of the students gained one mark for stating that the forces were equal in size or that they repelled, this being taken to mean that they act in opposite directions. Very few students made two valid points.
(b) The majority of students gained this mark.
E2.(a) About half of the students gained this mark.
(b) (i) About half of the students gained one mark for the idea that the bottles rubbed against the conveyor belt / guides. Few students went on to link this to the transfer of charge.
(ii) About half of the students were able to state what happens to change an atom into an ion.
(iii) Very few students gained this mark even though a simple answer like ‘the conveyor belt is rubber’ was sufficient.
E3. (a) (i) Few students scored the maximum mark for this part question. Although many students understood that the polystyrene beads became charged by friction with the plastic pipe, there was less understanding of the nature and origin of this charge. Having been informed that the beads were negatively charged when they left the pipe, there were many responses in terms of either the beads or the plastic pipe being negatively charged before they came into contact. There were too many answers in terms of ‘positive electrons’ or the transfer of protons /positive charge.
(ii) Many students were aware that the polystyrene beads were one of the control variables but far too many responses vaguely alluded to the amount of beads rather than the volume being used. Students that qualified ‘amount’ by adding 75 cm3gained the mark.
(b) (i) This part question was answered well with 83% of students giving the correct relationship.
(ii) Many students realised that a shortening of the pipe would lead to a decrease in the
charge. However fewer of the students were able to explain why. A significant number of students thought that the beads started with a charge and since they would be in the pipe for less time would transfer less of this charge and so arrived at the conclusion that the final charge would be greater.
(c) (i) Although many students chose the correct size of particles, few students were able to provide a scientific reason for their choice.
(ii) This part question was not well answered with far too many suggestions provided which would have involved a change to the industrial process. Many students chose to change the size of the particles but were divided as to whether it should be to larger or to smaller particles. Worryingly many students either wanted to change the plastic pipe for one made of an insulating material, or to a metal as it is a good insulator! The use of an earth wire was rarely seen.
(d) A small minority of students answered this correctly by stating that it allowed a comparison of the relative risks. Most students simply stated ‘fair test’ or listed a combination of the words accurate / precise/ reliable as a way of trying to cover all eventualities.
E4. (a) This straightforward question again caused students to struggle. The fact that it is electrons that transfer onto a substance to give it negative charge continues to be beyond many students. Often students described protons or positive electrons moving. The other area of confusion is that many students thought that the woollen cloth had an initial negative charge. The gain of negative charge by the rod was from this surplus charge on the wool.
(b) (i) Most students found this application of understanding question too challenging. The main area of confusion was what a balance actually measures i.e. the downward force placed on it. The usual attempt was in terms of transfer of extra charge, in a variety of forms, from the top rod to the bottom. This extra charge was detected by the balance as an increase in weight or mass. It was rare to see a correct answer.
(ii) Only about a tenth of students scored 1 mark for recognising that as the distance decreased the force increased. Often this mark was not given because students simply repeated, from the stem of the question, that the reading on the balance increased instead of stating that there was an increase in force. The essential extra bit of information that it was the charges producing the force was very rarely given.
E5. (a) Just over half of the candidates chose the correct statement.
(b) (i) The stem of this part question clearly stated that the movement of the plastic bottles
on the conveyor belt had caused the bottles to become charged so it was disappointing that there were so many responses which attributed the charge to having come from some process involving the ionised air. Very few candidates gained the mark for electron or charge transfer.
(ii) Hardly any candidates were able to say what an ion is. Nearly one-fifth of candidates opted to leave this part question blank.
(iii) Those candidates that gained a mark usually did so by realising that the belt was rubber / an insulator, but a considerable number of candidates argued that the charge continues to build up as the bottles are still rubbing against the guides. Some candidates wanted each bottle to be earthed and others claimed that ‘static isn’t electricity’.
E6. (a) Candidates were generally aware that the two materials rubbed together would create friction and the build up of static electricity. The award of the second mark was more problematical, as although many candidates understood that electrons were involved, the award of a mark was often negated by responses involving positive electrons or contradictions in the polarity of the materials after the movement of electrons. A significant number of candidates thought that protons were transferred.
(b) Over two thirds of candidates were able to pick the two correct statements, with a further third of candidates being able to pick one correct statement.
(c) (i) The majority of the candidates were aware that copper would be the choice of material for a lightning conductor because it, being a metal, would conduct electricity. However, some candidates, although receiving one mark for choosing copper, did not receive credit for their reason for their choice because their responses were in terms of heat conduction.
(ii) Few candidates scored this mark. Most candidates thought that the lightning conductor should have a higher resistance than the building.
(iii) The unpredictability of lightning storms was appreciated by most candidates who gained credit for stating the place, accompanying weather, timing and severity of the lightning strikes rendered a controlled experiment unlikely. The majority of the responses that did not gain credit were purely in terms of health and safety issues.
E7. (a) The majority of candidates scored all 3 marks.
(b) The majority of the candidates chose the refuelling of an aircraft as being potentially
hazardous due to a build up of static charge. Many candidates were then aware of the possibility of a spark igniting the flammable fuel. However, after ticking the correct situation, a significant number of candidates thought the danger lay in the form of electrocution of the ground staff or passengers.
E8. (a) This question was poorly answered with a small majority of the candidates scoring no marks. In some cases this was due to a lack of knowledge or understanding eg, candidates refer to the attraction of the (positive) boy’s body to the negative dome or to the movement of positive charge / protons / positive electrons.In many instances, a lack of precision in the use of English prevented candidates gaining marks, especially in respect of the second mark point where responses were left at hairs repelling without further explanation. Some candidates referred to hair standing on end as a result of the person getting a shock and others because the charge was trying to escape from the body.
(b) Under a quarter of the candidates scored 2 marks for a correct calculation. A significant number of candidates scored 1 mark for answers of either 2 or 0.002 as they had not converted the kV or mJ correctly, despite the information in the stem.A number of candidates did not seem to have access to a calculator and had done calculations around the text, sometimes making errors which deprived them of full marks. Of those who did not gain marks, this was evenly spread between those who did not transform the equation correctly and those who did not transform values properly. At this level it is disappointing that over a third of the entry simply multiplied the given numbers; with or without an attempted conversion.
(c) Only half of the candidates gave the correct answer.
E9. Foundation tier
This question was not well answered.
(a) Many responses considered charge leaking from the engine or the steering wheel. There was little idea of charging due to friction between the clothes and seat. One common answer was ‘Friction between the wheels and the road causes heat which is changed into static’. The Sun also seems to play a big part in the creation of static charge. A small minority of candidates explored the legal meaning of “being charged”.
(b) (i) Fair test was the most common incorrect answer. Some candidates considered the effect upon the driver’s comfort and safety of the hot and humid conditions.
(ii) This part of question 7 was answered better. Many candidates seemed aware of the limitations of the data.
Higher tier
(a) Many candidates had the idea of rubbing and friction being involved, but relatively few tied it down to the clothing of the driver and the seat. Many candidates had the idea of electron transfer, and quite a few at least mentioned transfer of charge.
(b) (i) Only the minority of candidates recognised that humidity or water vapour would affect the charge.
(ii) The majority of the candidates that scored credit did so by discussing the conditions of the test, relatively few referred to the limited range of materials tested. Of the former, several mentioned both humidity and temperature, but some lost credit through poor expression of the ideas.
E10. (a) (i) This was well answered with the majority of candidates choosing the correct responses.
(ii) About 75 % of candidates correctly said that the remaining charge would be positive. A few candidates gained credit for the answer proton.
(iii) This was question was generally answered correctly.
(b) (i) This should have been an easy question and it was for many candidates, but a significant number did choose plastic or rubber thinking that it was necessary to have an insulator to stop electricity (rarely current or charge) flowing to protect the worker and/or the chip. Most of the candidates correctly choosing copper also gave a correct reason. A few candidates did manage to think or mistakenly write that copper was an insulator.
(ii) About 75 % of candidates gave the correct answer.
