Physics Support Materials Higher Electricity and Electronics b Electric Fields and Resistors in Circuits 3,3, 4, 5, 6, 7, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,4,5,6,7,11,12,13,14,15,16, 17,18,19, 20,21,22,23,24,25,26,27,28,29,30, Click on a question number

Physics Support Materials Higher Electricity and Electronics  An electron volt is a unit of energy. It represents the change in potential energy of an electron which moves through a potential difference of 1 volt. If the charge on an electron is 1.6 x C, what is the equivalent energy in joules? 3 Electric Fields and Resistors in Circuits Click the mouse to continue

Physics Support Materials Higher Electricity and Electronics  Mass of an electron = 9.1 x  kg. Charge on an electron = 1.6 x C. The electron shown below is accelerated across a p.d. of 500 V. (a) How much electrical work is done? Electric Fields and Resistors in Circuits Click the mouse to continue 4 (b) How much kinetic energy has it gained? (c) What is its final speed?

Physics Support Materials Higher Electricity and Electronics  Electrons are ‘fired’ from an electron gun at a screen. The p.d. across the gun is 2000 V. After leaving the positive plate the electrons travel at a constant speed to the screen. Assuming the apparatus is in a vacuum, at what speed will the electrons hit the screen? Electric Fields and Resistors in Circuits Click the mouse to continue 5

Physics Support Materials Higher Electricity and Electronics  What would be the increase in speed of an electron accelerated from rest by a p.d. of 400 V? Electric Fields and Resistors in Circuits Click the mouse to continue 6

Physics Support Materials Higher Electricity and Electronics  An X-ray tube is operated at 25 kV and draws a current of 3 mA. (a) Calculate (i) the kinetic energy of each electron as it hits the target Electric Fields and Resistors in Circuits Click the mouse to continue 7 (b) What happens to the kinetic energy of the electrons? (ii) the velocity of impact of the electron as it hits the target (iii) the number of electrons hitting the target each second. It is transferred to the E k of the X ray photon

Physics Support Materials Higher Electricity and Electronics  In the circuit opposite: (a) what is the total resistance of the circuit Electric Fields and Resistors in Circuits Click the mouse to continue 11  (b) what is the resistance between X and Y  (c) find the readings on the ammeters  (d) calculate the p.d. between X and Y  (e) what power is supplied by the battery? The current splits in the ratio of 12 : 4 or 3 : 1 The current through the 4  resistor is 3/4 of 2 A or 1.5 A

Physics Support Materials Higher Electricity and Electronics  The circuit opposite uses the 230 V alternating mains supply. Find the current flowing in each resistor when: (a) switch S is open (b) switch S is closed. Electric Fields and Resistors in Circuits Click the mouse to continue 12

Physics Support Materials Higher Electricity and Electronics  An electric cooker has two settings, high and low. It takes 1 A at the low setting and 3 A at the high setting. Electric Fields and Resistors in Circuits Click the mouse to continue 13  (a) Find the resistance of R 1 and R 2  (b) What is the power consumption at each setting? At the low setting, the switch is open At the high setting, the switch is closed OpenClosed

Physics Support Materials Higher Electricity and Electronics  (a) Find the value of the series resistor which would allow the bulb to operate at its normal rating. Electric Fields and Resistors in Circuits Click the mouse to continue 14  (b) Calculate the power dissipated in the resistor Finding the current through the bulb The current through the bulb is the same as the current through the resistor

Physics Support Materials Higher Electricity and Electronics  In the circuit below, r represents the internal resistance of the cell and R represents the external resistance of the circuit. When S is open, the voltmeter reads 2.0 V. When S is closed, it reads 1.6 V and the ammeter reads 0.8 A. Electric Fields and Resistors in Circuits Click the mouse to continue 15  (a) What is the e.m.f. of the cell?  (b) What is the terminal potential difference when S is closed?  (c) Calculate the values of r and R.  (d) If R was halved in value, calculate the new readings on the ammeter and voltmeter.

Physics Support Materials Higher Electricity and Electronics  The cell in the diagram has an e.m.f. of 5 V. The current through the lamp is 0.2 A and the voltmeter reads 3 V. Calculate the internal resistance of the cell. Electric Fields and Resistors in Circuits Click the mouse to continue 16

Physics Support Materials Higher Electricity and Electronics  A cell of e.m.f. 4 V is connected to a load resistor of 15 . If 0.2 A flows round the circuit, what must be the internal resistance of the circuit? Electric Fields and Resistors in Circuits Click the mouse to continue 17

Physics Support Materials Higher Electricity and Electronics  A signal generator has an e.m.f. of 8 V and internal resistance of 4  A load resistor is connected to its terminals and draws a current of 0.5 A. Calculate the load resistance. Electric Fields and Resistors in Circuits Click the mouse to continue 18

Physics Support Materials Higher Electricity and Electronics  (a) What will be the terminal p.d. across the cell in the circuit below. Electric Fields and Resistors in Circuits Click the mouse to continue 19  (b) Will the current increase or decrease as R is increased?  (c) Will the terminal p.d. then increase or decrease? Explain your answer. As R increases, the current decreases The t.p.d. increases because the lost volts will be smaller.

Physics Support Materials Higher Electricity and Electronics  A cell with e.m.f. 1.5 V and internal resistance 2   is connected to a 3  resistor. What is the current? Electric Fields and Resistors in Circuits Click the mouse to continue 20

Physics Support Materials Higher Electricity and Electronics  A pupil is given a voltmeter and a torch battery. When he connects the voltmeter across the terminals of the battery it registers 4.5 V, but when he connects the battery across a 6   resistor, the voltmeter reading decreases to 3.0 V. (a) Calculate the internal resistance of the battery. Electric Fields and Resistors in Circuits Click the mouse to continue 21  (b) What value of resistor would have to be connected across the battery to reduce the voltage reading to 2.5 V ?

Physics Support Materials Higher Electricity and Electronics  In the circuit shown, the cell has an e.m.f. of 6.0 V and internal resistance of 1 . When the switch is closed, the reading on the ammeter is 2 A. What is the corresponding reading on the voltmeter ? Electric Fields and Resistors in Circuits Click the mouse to continue 22

Physics Support Materials Higher Electricity and Electronics  In order to find the internal resistance of a cell, the following sets of results were taken. Electric Fields and Resistors in Circuits Click the mouse to continue 23  (a) Draw the circuit diagram used.  (b) Plot a graph of these results and from it determine (i) the e.m.f. (ii) the internal resistance of the cell.

Physics Support Materials Higher Electricity and Electronics Electric Fields and Resistors in Circuits Click the mouse to continue 23(cont)  (c) Use the e.m.f. from part (b) to calculate the lost volts for each set of readings and hence calculate 6 values for the internal resistance.  (d) Calculate the mean value of internal resistance and the approximate random uncertainty.

Physics Support Materials Higher Electricity and Electronics  The voltage across a cell is varied and the corresponding current noted. The results are shown in the table below. Plot a graph of V against I. Electric Fields and Resistors in Circuits Click the mouse to continue 24  (b) Calculate the internal resistance.  (a) What is the open circuit p.d? Open circuit p.d. is voltage when no current is drawn

Physics Support Materials Higher Electricity and Electronics Electric Fields and Resistors in Circuits Click the mouse to continue 24 cont  (c) Calculate the short circuit current.  (d) A lamp of resistance 1.5   is connected across the terminals of this supply. Calculate (i) the terminal p.d.and (ii) the power delivered to the lamp.

Physics Support Materials Higher Electricity and Electronics  Calculate the p.d. across R 2 in each case. Electric Fields and Resistors in Circuits Click the mouse to continue 25

Physics Support Materials Higher Electricity and Electronics  Calculate the p.d. across AB (voltmeter reading) in each case. Electric Fields and Resistors in Circuits Click the mouse to continue 26 Potential at A = 6 V Potential at B = 3 V p.d. across AB = 3 V Potential at A = 2/7 x 5 = 1.4 V Potential at B = 8/18 x 5 = 2.2 V p.d. across AB = V Potential at A = 2/5 x 10 = 4 V Potential at B = 4/10 x 10 = 4 V p.d. across AB = 0

Physics Support Materials Higher Electricity and Electronics  (a) Calculate the reading on the voltmeter. Electric Fields and Resistors in Circuits Click the mouse to continue 27  (b) What alteration could be made to balance the bridge circuit ? Potential at A = 6/15 x 9 = 3.6 V Potential at B = 3/9 x 9 = 3 V p.d. across AB = 0.6 V Increase the 9 k  resistor to 12 k 

Physics Support Materials Higher Electricity and Electronics  Three pupils are asked to construct balanced Wheatstone bridges. Their attempts are shown. Electric Fields and Resistors in Circuits Click the mouse to continue 28  (a) Identify each circuit.  One of the circuits gives a balanced Wheatstone bridge, one gives an off - balance Wheatstone bridge and one is not a Wheatstone bridge.  (b) How would you test that balance had been obtained?  (c) In the off – balance Wheatstone bridge (i) calculate the potential difference across the galvanometer. Unbalanced Wheatstone Balanced Wheatstone Non Wheatstone The galvo should read zero in a balanced Wheatstone Bridge Potential at A = 5/15 x 1.5 = 0.5 V Potential at B = 10/15 x 1.5 = 1 V p.d. across AB = 0.5 V From B to A  (ii) in which direction will electric current flow through the galvanometer?

Physics Support Materials Higher Electricity and Electronics  Calculate the value of the unknown resistor X in each case. Electric Fields and Resistors in Circuits Click the mouse to continue 29

Physics Support Materials Higher Electricity and Electronics  The circuit shown opposite is balanced. Electric Fields and Resistors in Circuits Click the mouse to continue 30  (a)What is the value of resistance X?  (b) Will the bridge be unbalanced if (i) a 5  resistor is inserted next to the 10  resistor (ii) a 3 V supply is used.?  (c) What is the function of resistor R and what is the disadvantage of using it as shown? The bridge will be unbalanced if the resistance is increased to 15  The bridge will still be balanced if the supply voltage is changed The resistor R protects the sensitive galvo from large currents. In series the resistor reduces the sensitivity of the galvo