The diagram shows a negatively charged plastic rod held near to a thin stream of water. The water is attracted towards the rod.

Transcription

1 Current electricity exam qs C grade Madeley High School Q.(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. () (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. Page

2 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. (2) What happens to the structure of an atom to change the atom into an ion? () (iii) Earthing the conveyor belt with a conducting wire would not have solved this problem. Give a reason why. () (Total 5 marks) Page 2

3 Q2. (a) The diagram shows the voltage-current graphs for three different electrical components. Which one of the components A, B or C could be a 3 volt filament lamp? Explain the reason for your choice (3) (b) Using the correct symbols draw a circuit diagram to show how a battery, ammeter and voltmeter can be used to find the resistance of the wire shown. (3) (c) When correctly connected to a 9 volt battery the wire has a current of 0.30 amperes flowing through it. (i) Give the equation that links current, resistance and voltage.... () Page 3

4 Calculate the resistance of the wire. Show clearly how you work out your answer and give the unit Resistance =... (3) (iii) When the wire is heated, the current goes down to 0.26 amperes. State how the resistance of the wire has changed () (Total marks) Q3.(a) The diagram shows the circuit used to investigate the resistance of a sample of a material. The diagram is not complete; the ammeter and voltmeter are missing. (i) Draw the symbols for the ammeter and voltmeter on the diagram in the correct places. (2) How can the current through the material be changed? () Page 4

5 (b) Madeley High School The material, called conducting putty, is rolled into cylinders of different lengths but with equal thickness. Graph shows how the resistance changes with length. Length in centimetres (i) The current through a 25 cm length of conducting putty was 0.5 A. Use Graph to find the resistance of a 25 cm length of conducting putty. Resistance =... ohms () Use your answer to (b) (i) and the equation in the box to calculate the potential difference across a 25 cm length of conducting putty. potential difference = current x resistance Show clearly how you work out your answer. Potential difference =... volts (2) Page 5

6 (c) A second set of data was obtained using thicker pieces of conducting putty. Both sets of results are shown in Graph 2. Length in centimetres (i) What is the relationship between the resistance and the thickness of the conducting putty? () Name one error that may have reduced the accuracy of the results. () (iii) How could the reliability of the data have been improved? () (Total 9 marks) Page 6

7 Q4. (a) The circuit diagram drawn below includes a component labelled X. Madeley High School (i) Use the equation in the box to calculate the potential difference across the 8 ohm resistor. potential difference = current resistance Show clearly how you work out your answer Potential difference =... volts (2) (b) What is the potential difference across component X?... The graph shows how the resistance of component X changes with temperature. () (i) What is component X?... () Page 7

8 Over which range of temperatures does the resistance of component X change the most? Madeley High School Put a tick ( ) next to your choice. 0 C to 20 C 20 C to 40 C 40 C to 60 C 60 C to 80 C 80 C to 00 C () (Total 5 marks) Q5. The current through component X is measured when different voltages are applied across it. (a) Name the component labelled Y in the circuit.... () (b) What type of meter is Z?... () Page 8

9 (c) The table shows the measurements obtained in this experiment. Madeley High School Voltage in V Current in ma Draw a graph of the measurements. (2) (d) Use the shape of the graph to name component X.... () (Total 5 marks) Page 9

10 Q6. The drawing shows the circuit used to investigate how the current through a 5 ohm (Ω) resistor changes as the potential difference (voltage) across the resistor changes. (a) Draw, in the space below, a circuit diagram of this circuit. Use the correct symbols for each part of the circuit. (2) (b) (i) Write down the equation that links current, potential difference and resistance.... () Page 0

11 Calculate the potential difference across the 5 ohm (Ω) resistor when the current through the resistor equals 0.4 A. Show clearly how you work out your final answer potential difference =... volts (2) (iii) Complete the graph to show how the current through the resistor changes as the potential difference across the resistor increases from 0 V to 3 V. Assume the resistor stays at a constant temperature. (2) (c) The resistor is replaced by a 3 V filament lamp. The resistance of the lamp increases as the potential difference across it increases. Why? () (Total 8 marks) Page

12 Q7.The diagram shows the circuit set up by a student. Madeley High School (a) The student uses the circuit to test the following hypothesis: The current through a resistor is directly proportional to the potential difference across the resistor. (i) If the hypothesis is correct, what should the student predict will happen to the current through the resistor when the potential difference across the resistor is doubled? () Name the component in the circuit used to change the potential difference across the resistor. () (b) The student used the data obtained to plot the points for a graph of current against potential difference. Page 2

13 (i) Why has the student plotted the points for a line graph and not drawn a bar chart? () One of the points has been identified by the student as being anomalous. What is the most likely cause for this anomalous point? () (iii) Draw a line of best fit for these points. () (iv) Does the data the student obtained support the hypothesis? Give a reason for your answer. () (Total 6 marks) Page 3

14 Q8. A student designed the circuit below to measure temperature using a thermistor. To calibrate the thermistor to measure temperature, the student placed the thermistor in a beaker of water at 0 C and took the voltmeter reading. The student then heated the water slowly with a Bunsen burner. The student recorded the reading on the voltmeter every 0 C. (a) (i) Before calibrating the thermistor the student completed a risk assessment. Write down one possible hazard that the student should have written in the risk assessment and what the student should do to reduce the risk of the hazard causing an injury. (2) At 0 C the reading on the ammeter is 0.5 A. Calculate the reading on the voltmeter at 0 C. Write down the equation you use, and then show clearly how you work out your answer. Voltmeter reading =... V Page 4

15 (2) (b) Most of the readings taken by the student are displayed in the graph. (i) Explain why the reading on the voltmeter changes when the temperature of the water increases. (3) What is the temperature interval that can be measured with this circuit? Page 5

16 Madeley High School () (iii) Once calibrated, between which temperatures would this circuit give the greatest resolution for temperature readings? Tick ( ) one box. 20 C to 40 C 40 C to 60 C 60 C to 80 C Give a reason for your answer. (2) (c) Thermistors have many practical uses, including being used as a thermometer to measure temperature. Give one other practical use for a thermistor () (Total marks) Page 6

17 Current electricity exam qs C grade M.(a) 3 rd box The negative charge in the water is repelled by the rod and the positive charge is attracted to the rod. (b) (i) friction between bottles and conveyor belt / (plastic) guides accept bottles rub against conveyor belt / (plastic) guides charge transfers between bottles and conveyor belt / (plastic) guides accept specific reference eg electrons move onto / off the bottles reference to positive electrons / protons negates this mark (the atom) loses or gains one (or more) electrons (iii) charge will not (easily) flow off the conveyor belt / bottles accept the conveyor belt / bottles is an insulator / not a conductor accept conveyor belt is rubber [5] M2. (a) C award mark if A and B identified as not filament lamp resistance increases negated by wrong statement e.g. current goes down as the lamp gets hot accept as current (through lamp) or voltage (across lamp) increases do not accept non-ohmic reason independent of choice of Page 7

18 component Madeley High School (b) ammeter wire and battery only in series non standard symbols acceptable if correctly identified (labelled) for ammeter, voltmeter and battery voltmeter only in parallel with wire or battery all in series or ammeter in parallel neither of these two marks awarded all symbols correct ignore lines drawn through centres of symbols (c) (i) voltage = current resistance accept V = I R accept volts = amps ohms do not accept V = C R accept if subsequent method correct 30 accept correct substitution for mark (9/0.3) 2 ohms accept correct symbol Ω (iii) goes up must be a comparison accept calculation if answer is larger than c [] Page 8

19 M3.(a) (i) ammeter symbol correct and drawn in series accept do not accept lower case a voltmeter symbol correct and drawn in parallel with the material do not accept adjust / use the variable resistor accept change the resistance orchange the number of cells accept battery for cell accept change the pd / accept change the voltage accept increase / decrease for change (b) (i) 37.5 (Ω) accept answer between 36 and 39 inclusive 5.6(25) or their (b)(i) 0.5 allow mark for correct substitution ie 37.5 or their (b)(i) 0.5 provided no subsequent step shown 2 (c) (i) the thicker the putty the lower the resistance answer must be comparativeaccept the converse Page 9

20 any one from: measuring length incorrectly accept may be different length measuring current incorrectly do not accept different currents measuring voltage incorrectly do not accept different voltage ammeter / voltmeter incorrectly calibrated Madeley High School thickness of putty not uniform do not accept pieces of putty not the same unless qualified meter has a zero error do not accept systematic / random error accept any sensible source of error eg putty at different temperatures do not accept human error without an explanation do not accept amount of putty not same (iii) repeat readings and take a mean accept check results againaccept do experiment againaccept do it again and take mean(s) accept compare own results with other groups do not accept take more readings [9] M4. (a) (i) 4 (V) allow mark for correct substitution 2 5 (V) or (9 their (a)(i)) correctly calculated e.c.f do not allow a negative answer (b) (i) thermistor c.a.o 0 C to 20 C [5] Page 20

21 M5. (a) variable resistor accept rheostat (b) voltmeter (c) straight line correct between 0.2 and 0.8 if line incorrect, or no line, and correct plots 0.2 to 0.8 award mark 2 (d) diode / rectifier [5] M6. (a) all symbols correct accept push switch symbol switch may be open or closed any lines through symbols = 0 marks correct circuit drawn polarity of cells not relevant provided they are joined correctly voltmeter must be across resistor only two cells are required in the diagram ignore the order of the components allow small gaps in circuit omission of any component = 0 marks Page 2

22 (b) (i) potential difference = current resistance accept voltage or p.d. for potential difference accept V= I R Madeley High School accept provided I R subsequent use correct do not accept C for current 2 allow mark for correct substitution wrong working loses both marks 2 (iii) straight line drawn through the origin judge by eye straight line passes through I = 0.4, V = their (b) / 2 and 0.0 this mark may be awarded if all points shown including these points are correct even if no line is drawn N.B. a curve scores 0 marks (c) temperature increases accept filament lamp / it gets hotter allow heat for temperature [8] M7. (a) (i) also double increases is insufficient variable resistor accept rheostat / potentiometer Page 22

23 (b) (i) the data / results / variables are continuous accept data / results / variables are not categoric / discrete misreading the ammeter do not accept misreading the meter / results do not accept misreading the ammeter and / or voltmeter reading / human error is insufficient (iii) straight line from the origin drawn passing close / through points at V, 5 V, 6 V and ignoring anomalous point do not accept line drawn dot-to-dot (iv) yes mark is for the reason supports predictionor(straight) line passes through the origin accept a mathematical argument, eg when p.d. went from 2 to 4 the current went from 0.3 to 0.6 it s directly proportional is insufficient [6] M8. (a) (i) spilling boiling / hot water accept any sensible suggestion suitable precaution to reduce risk from hot water eg clamp the probe / complete the experiment standing accept any sensible answer but must be linked to the named risk 3 (V) allow mark for substitution into correct equation Page 23

24 ie Madeley High School 2 (b) (i) resistance of thermistor decreases therefore the current in the circuit increases causing a bigger share of the p.d. across 6 Ω resistor 0 00 ( C) accept 0 00 C (iii) 20 C to 40 C because a small temperature change gives a bigger voltmeter reading change (c) thermostat accept a correct description of a use [] Page 24