topic 10 Flashcards
a resistor is connected to a power supply
potential difference = 6.0V
which corresponds to this?
A) 6.0 joules per ohm
B) 6.0 amps per coulomb
C) 6.0 joules per coulomb
D) 6.0 amps per ohm
C - 6.0 joules per coulomb
current = 200mA
total charge = 42C
calculate time taken for this amount of charge to flow through resistor
42 = 200 x t / 1000
t = 42 x 1000 / 200 x 60
t = 3.5
calculate total energy transferred by 6.0V power supply when a charge of 42C flows through resistor
E = 42 x 60
= 250
the resistor becomes warm while there is a current in it explain why
collisions between electrons so the lattice moves more
figure 16 - cardboard tube with wire coming out each end
two 10 ohm resistors inside cardboard tube.
potential difference of 6.0V connected between P and Q
current of 1.2A in wires
deduce how the resistors have been arranged in cardboard tube
R between P and Q = 6 / 1.2 = 5 ohms
this is less than a single resistor so resistors must be connected in parallel
figure 18 - 8 filament lamps connected together to a 12V power supply
calculate potential difference across each lamp
V = I x R
12 / 8 = 1.5
figure 18 - 8 filament lamps connected together to a 12V power supply
power output of each lamp in 0.75W
calculate resistance of each lamp
I = 0.75 / 1.5 = 0.5
R = 1.5 / 0.5 = 3
= 3 ohms
explain with aid of circuit diagram a method a student could use to investigate how the resistance of a single lamp changes with the potential difference across the lamp
parallel diagram (look on topic F questions)
firstly set up equipment as shown in the diagram. then measure the reading on the ammeter to find out the size of the circuits current. next, measure the voltage on the voltmeter. calculate the resistance with R = V / I . gradually change the amount of voltage supplied into the circuit and continue the calculations. plot the recordings on a graph
‘ the resistance of the lamp is directly proportional to the potential difference’
comment on the conclusion using figure 5 to help
resistance increases with potential difference. for example doubling the resistance doesnt double the potential difference
describe how the student could add a component to the circuit that would provide a continuously variable voltage across the lamp
add a variable resistor in series (with power supply)
state the measurements that the student must take to find the overall resistance of the resistors in parallel
voltage and current
current in element of immersion heater is 14A
power of immersion heater is 130W
calculate resistance of immersion heater to 2 sf
p = i^2 x r 130 = 14^2 x r
r = 130 / 14^2
= 0.66
the current in the heating element of the kettle is 8.3A.
state two differences between the movement of charge in the heating element of the kettle and the movement of charge in the immersion heater
1 - rate of charge in immersion heater is greater than in the kettle
2 - direction of flow of charge in kettle changes but it stays the same in the immersion heater
3 pin plug used to connect kettle to the mains. a fault occurs in the kettle causing the live wire to touch the metal case of the kettle.
explain how the safety features of the plug operate when this fault occurs
earth wire connected to metal case which is a conductor. when the live wire touches the case the resistance between the live and earth is very low and a very large current flows to earth through low resistance earth wire. the case is kept at the same potential as earth so cannot get a shock if a person touches the metal case. fuse is made of thin wire and this connected between live pin and wire. fuse can prevent damage to house wiring as it disconnects main supply to kettle when temperature goes beyond melting point
comment on the relationship between the overall resistance of the circuit and the number of resistors in parallel using figure 20 to support your answer
the overall resistance decreases as the number of resistors in parallel increases. the relationship is non linear. this is shown by the resistance being 1 at 1 and 0.2 at 5
