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P6 Flashcards

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1
Q

What is the definition for a ‘resistor’?

A

a resistor in a circuit resists the flow of the current

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2
Q

What is a variable resistor?

A

a resistor that can have its resistance changed

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3
Q

What can a variable resistor be used for?

A
  • controlling the current (increasing the resistance results in a lower current)
  • varying the brightness of a bulb (a higher current makes the bulb brighter)
  • varying the speed of a motor (higher current results in a greater speed in the motor
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4
Q

How is the resistance altered in a variable resistor?

A
  • the length of the wire is changed (a longer wire creates a higher resistance and therefore a lower current)
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5
Q

What 3 units are used for electrical currents?

A
  • voltage (measured in volts - V)
  • current (measured in amps - A)
  • resistance (measured in ohms)
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6
Q

What happens to the resistance and the current when a wire gets hot?

A

the resistance increases and therefore the current decreases

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7
Q

What is the equation for resistance?

A

voltage X current

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8
Q

What does the gradient on a voltage-current graph show?

A

the resistance

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9
Q

What is the job of a resistor in a circuit?

A

it is there to stop or slow the flow of the current and therefor decreasing the voltage

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10
Q

What does Rt stand for?

A

total resistance

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11
Q

How do you find the total resistance of a circuit when there are more than one resistors in use?

A

add up all of the individual resistances together e.g Rt = R1 + R2 + R3 + R4

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12
Q

What do resistors in parallel do to the overall resistance of the circuit?

A

decrease the resistance

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13
Q

How do you calculate the total resistors when one or more resistors are used and they are in parallel?

A

1/Rt = 1/R1 + 1/R2 + 1/R3

THE ANSWER MUST BE INVERTED otherwise it will just be 1/Rt it needs to be for example; Rt/1 = 10/5 = 2

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14
Q

What are potential dividers and what are the made from?

A

potential dividers are circuits that produce a required voltage (also known as the potential difference)
these are made form fixed resistors

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15
Q

What happens if the value of R2 is much greater than the value of R1?

A

the output will be approximately V (the input voltage)

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16
Q

What happens if the value of R2 is much less than the value of R1?

A

the output will be close to zero

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17
Q

What happens if you change the fixed resistors in R1 and R2 to variable resistors?

A

you are able to adjust the output voltage

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18
Q

What is the equation to find the Vout (voltage output)?

A

(R2 / (R1 + R2)) X Vin

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19
Q

What is an LDR and what does it stand for?

A

LDR stand for light dependant resistor

it changes its resistance in response to light levels

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20
Q

What is a thermistor?

A

a thermistor is a resistor that changes its resistance according to the temperature

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21
Q

What is a transistor? What are the 3 things it consists of?

A

a transistor is basically a switch

- it consists of a base, a collector and an emitter

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22
Q

What is the equation for the current through an emitter in a transistor?

A

base current + collector current = emitter current

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23
Q

How can transistors be connected together?

A

with logic gates

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24
Q

What are the 2 different types of input to a logic gate?

Study These Flashcards
A

a high voltage (about 5V) - called high = 1 (on)

a low voltage (about 0V) - called low = 0 (off)

25
What is the letter for output in a logic gate?
Q
26
What does a NOT gate do?
gives out the opposite charge - if input is on output is off - if input is off then output is on
27
What does an AND gate do?
will only work if both inputs are on
28
What does an OR gate do?
the only time it wont work is if both inputs are off - if input 1 is on and input 2 is off then the output will be on - if input 1 is off and input 2 is on then the output will be on - if both inputs are on then the output will be on
29
What does a NAND gate do?
(think of No AND meaning its the opposite of AND) | the output is only off when BOTH inputs are on (opposite to an AND gate)
30
What does a NOR gate do?
(think of No OR meaning its the opposite of OR) | the output is only on when BOTH inputs are off (the opposite to an OR gate)
31
What is a relay used for in logic gates?
it is used to isolate a low voltage from the high voltage mains to give to the logic gates
32
What are the circles called in a magnetic field?
concentric circles
33
What concentric circles are there in a magnetic rectangular coil?
straight lines through the middle and circles around the sides
34
What is a solenoid?
a circular coil of wire.. like a spring
35
What concentric circles are there in a magnetic solenoid?
just a massive circle along the top and bottom of the wire
36
What is the motor-effect?
when a current carrying wire is placed in a magnetic field and then experiences a force from it causing it to move
37
What is Flemings left hand rule?
- first finger = direction of the magnetic field - second finger = direction of the current - thumb = direction of force e.g which way it turns
38
How do DC motors work?
- the current flowing through the coil creates a magnetic field - the magnetic field of he coil and the magnet interact - each side of the coil experiences a force in the opposite direction because the current is flowing in opposite directions in the 2 parts of the coil - the forces combine to make the coil rotate
39
What is a split ring commutator?
this changes the direction of the current in the coil every half a turn this happens due to the bits of wire balancing in the split ring commutator making sure that they move as the coil does too
40
What is a radial field?
the maximum force (more movement of the coil and therefore more electricity) is produced when the coil and the magnetic field are at right angles to each other
41
Why are curved pole pieces used to make radial fields?
because when the magnetic field connects with the side of the pole, it makes a right angle which is the strongest angle to produce a radial field
42
When is a split ring commutator used in generators?
in a DC generator
43
What is the alternative to a commutator that are used in an AC generator?
a slip ring and brushes
44
How do AC generators work?
- as the wire moves up (e.g turns) a current is induced in the wire - because the wire has turned, a current has been induced in the wire in the opposite direction (as the wire is now on the opposite pole side) which produces an alternating current this is how an AC generator ensures that the current changes direction every half a turn
45
How do the brushes in the slip rings in AC generators work?
the brushes are made out of carbon which means that when the coil turns around they make contact with the slip rings enabling the current to flow while the coil is rotating freely
46
How do you increase the voltage when using a coil and a magnet?
- increase the speed at which the magnet or the coil moves - increase the number of turns on the electromagnets coils - increasing the strength of the magnetic field e.g getting a stronger magnet
47
What is a transformer?
this is 2 separate coils of wire around an iron core which creates a magnetic field because the 2 wires aren't connected, the magnetic field helps induce the current in both of the wires resulting in an alternating current it only works with AC not DC
48
What are step-up transformers?
they increase the voltage from the mains
49
What are step-down transformers?
they decrease the voltage from the mains
50
How do we reduce the loss of heat in overhead power cables? How is this done physically?
decreasing the current | we increase the voltage which therefore decreases the current
51
When do we use step-up transformers?
in the power stations for the national grid to increase the voltage and therefore decrease the current
52
What are isolating transformers?
this is when the coils in the transformer aren't connected together this makes it safer in bathrooms as they are isolated from the mains supply it has the same number of turns on the primary and secondary coils
53
What is a silicon diode?
something that allows the current to flow through it in one direction only
54
What is a silicon diode made of?
2 types of silicon: n-type (which contains extra electrons and is therefore negatively charged) p-type (which has holes in where there should be electrons so it is positively charged)
55
When will a diode allow the current to pass through?
when the diode is forwards biased e.g when the n-type is connected to the negative side of the battery not when the diode is reverse biased because the electrons drop into the holes
56
What is half-wave rectification?
this is when an alternating current only passes through one single diode which means that the diode wont let the current alternate meaning it only passes through one way but stops to try and get back meaning there are interferences
57
What is full-wave rectification?
this is when a group of 4 diodes is used to make a bridge circuit
58
What is a capacitor?
this is something that can store charge and can discharge it later
59
What is smoothing? How does it work?
this is when a capacitor is attached to an unsteady voltage supply e.g full-wave rectification and can therefore be smoothed to become a DC it works by discharging when the voltage starts to fall low giving the circuit more of a charge and then when the voltage is high enough again it charges up the capacitor and the cycle starts again

Physics (6 decks)

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