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physics (paper one) > electrical circuits (topic 2) > Flashcards

electrical circuits (topic 2) Flashcards

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1
Q
A
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2
Q

calc the pd across the lamp (pd = current x resistance) current is 0.02A

A

0.02 x 150 = 3V

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3
Q

calc the pd across the resistor, pd of lamp is 3

A
  • potential difference across lamp + potential difference across resistor = 12 V
  • 3 (voltage of lamp) + voltage across resistor = 12 V
  • voltage across resistor = 12 - 3 = 9V
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4
Q

state the reading on the voltmeter

A

10

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5
Q

state the voltage across the 300Ω resistor

A

10

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6
Q

calculate the current through the 200Ω resistor, current = pd/resistance

A

10/200 = 0.05A

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7
Q

the 300 Ω resistor has a current of 33.3 mA flowing through it, calculate the total circuit current
(0.05 is the current through the 200 resistor)

A
  • total circuit current = current through 200 Ω + current through 300 Ω
  • total circuit current = 0.05 + 0.0333 = 0.0833 A
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8
Q
A
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9
Q

explain why the student uses a variable resistor and not a fixed resistor (2) (a student is investigating the current-voltage characteristic of a filament lamp)

A
  • variable resistor allows the circuit resistance to vary
  • varying the circuit resistance allows the current to be varied
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10
Q

describe what happens to the resistance of the lamp as the voltage is increased from 0V to 10V

A
  • between 0 V and 4 V, the current increases linearly
  • constant resistance between 0 V and 4 V
  • between 4 V and 10 V, the current increases at a decreasing rate
  • resistance increases between 4 V and 10 V
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11
Q

pd = current x resistance

A
  • 12 - 5
  • 7/350 = 0.02A
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12
Q

the student moves the circuit into a warmer room, describe what happens to the voltage across the lamp, you may assume the resistance of the lamp stays constant (3)

A
  • resistance of thermistor decreases (resistance of a thermistor decreases as temp increases)
  • circuit current increases
  • potential difference across lamp increases
  • potential difference across thermistor decreases
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13
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14
Q
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15
Q

explain what is meant by a D.C. power supply (2)

A
  • direct current
  • current flows continuously around circuit in the same direction
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16
Q

a student is investigating how the resistance of a wire varies with length, explain why the student must turn the power supply off between readings (3-

A
  • when a current flows through the wire it causes it to heat up
  • turning off the power supply between readings reduces the heating effect of the current
  • an increase in temperature would increase the resistance of the wire
17
Q

a student is investigating how the resistance of a wire varies with length, describe how the student could use the circuit to identify the relationship between length and resistance (6)

A
  • using a ruler and crocodile clips, set the length of wire to 10 cm
  • turn on power supply and record voltage and current values
  • turn off power supply and increase length of wire by 5 cm
  • repeat experiment and calculate average values
  • resistance = voltage/current
  • plot a graph of length against resistance
18
Q

the student concludes that resistance is directly proportional to the length of the wire, using data from the graph, show that resistance is directly proportional to length (3)

A
  • resistance/length = constant
  • use of one set of values to calculate constant = 2 eg 60/30
  • use of second set of values to calculate constant = 2 eg 90/45
  • constant is the same, therefore resistance is directly proportional to length
19
Q
A
  • ammeter reading = total circuit current - current through top branch
  • ammeter reading = 2.66 - 0.66 = 2A
20
Q

the student opens the switch, describe what happens to the reading on the ammeter and the voltmeter

A
  • ammeter reading drops to zero as no current flows through the bottom branch
  • voltmeter reading is unchanged
21
Q

calculate the reading on the voltmeter

A
  • voltage = current x resistance
  • v = 0.66 x 5 = 3.33
22
Q

the 10 Ω resistor is replaced with a thermistor, the student places the circuit in a cold room, describe how the voltmeter and ammeter reading will change (4)

A
  • ammeter reading will remain the same
  • resistance of thermistor increases
  • lower current through top branch
  • potential difference across the 5 Ω resistor decreases/voltmeter reading decreases
23
Q

define current

A

the rate of flow of charge

24
Q

a filament lamp has a current of 275 mA flowing through it for 2 hours, calculate the charge that flows through the filament lamp

A
25
Q

the filament lamp is connected to a 10 V cell, calculate the energy transferred to the filament lamp in 2 hours (charge is 1980 C)

A
26
Q
A
  • current through S = total circuit current - current through R
  • current through S = 325 - 200 = 125 mA
27
Q

(current flowing through S is 125mA, 0.125A)

A
28
Q

calculate the potential difference across T (pd across S = 2.5)

A
  • potential difference across T + potential difference across S = 10 V
  • potential difference across T = 10 - 2.5 = 7.5 V
29
Q

calculate the resistance of T at this temperature (voltage = 7.5)

A
30
Q

the student moves the circuit into a warm room, describe what happens to the potential difference across T

A
  • thermistor resistance decreases
  • current through S and T increases
  • higher potential difference across S
  • lower potential difference across T
31
Q
A
32
Q

describe the shape of the I-V graph (3)

A
  • no current when a negative voltage is applied
  • diode begins to conduct after 0.6 V
  • above 0.6 V current increases linearly
33
Q

when the voltage across the diode is 1.2 V, the current flowing through it is 17.6 mA, alculate the resistance of the resistor ?????

A
34
Q
A

all turned off

35
Q

describe the changes the student would need to make to the switches to turn on bulbs 3 and 4 (1)

A

both switches C and D would need to be closed

36
Q

explain the advantage of using parallel circuits for lighting control (2)

A
  • if the bulb blows in one branch, the other branch will still operate normally
  • light bulbs can be switched on/off independently
37
Q
  • the student closes switch A and B
  • after a short period of time the bulbs stop working
  • the student suspects that only one of the bulbs has blown
  • describe how the student could identify which bulb has blown (4)
A
  • close switches C and D and ensure both bulbs light
  • open switch C and replace bulb 3 or 4 with bulb 1
  • close switch C. If bulb 1 does not light, it has blown
  • repeat for bulb 2

physics (paper one) (25 decks)

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