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Physics - IGCSE > Ch 19 - (Electrical Circuits) > Flashcards

Ch 19 - (Electrical Circuits) Flashcards

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1
Q

What are power supplies?

A

cells, batteries, power supplies and generators all supply current to the circuit

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2
Q

What are resistors?

A

potential dividers, fixed and variable resistors, thermistors and light dependent resistors (LDR’s) control current

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3
Q

What are meters?

A

ammeters and voltmeters are used to measure the current and potential difference

  • Ammeters in series
  • Voltmeters in parallel
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4
Q

What are electromagnetic components?

A

Magnetizing coils, relays, and transformers use electromagnetic effects

  • relay use small current in one circuit to switch on another
  • transformers ‘step up’ and ‘step down’ current and potential difference.
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5
Q

What are fuses?

A

Protect expensive components from current surges and act as safety measures against fire

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6
Q

What are thermistors?

A
  • non - ohmic conductor
  • temperature dependent resistor
  • resistance changes based on temp
  • as temp increases, resistance of thermistor decreases
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7
Q

What are light - dependent resistors?

A
  • non-ohmic conductor
  • sensory resistor
  • resistance changes depending on light intensity (illumination)
  • as light intensity increases, resistance of LDR decreases
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8
Q

What is a diode?

A

allows a current in one direction

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9
Q

What happens if diode is placed in a.c. ?

A

Only allows a current half of the time (called as rectification)

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10
Q

How is the current in a series circuit? And why?

A
  • same value at any point
  • no. of electrons passing through per sec is same ate very part
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11
Q

What does the current flowing around series circuit depend on?

A
  • Voltage of power source
  • resistance of components in a circuit
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12
Q

What does increasing voltage do in a series circuit?

A

drives more current around the circuit

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13
Q

What does increasing number of components do in a series circuit?

A

increases the total resistance

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14
Q

What is the advantage in a parallel circuit?

A
  1. The components can be individually controlled, using their own switches
  2. If one component stops working the others will continue to function
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15
Q

How does Curr not flow in a parallel circuit?

A
  • In a parallel circuit, the current splits up
  • current in each branch will be smaller than the current from the power supply
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16
Q

What happens at every junction in parallel circuit and why?

A

-The current is conserved

  • amount of current flowing into the junction is equal to the amount of current flowing out of it
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17
Q

Why does current split up in junctions?

A

charge is conserved

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18
Q

What happens when current does not split up equally at junctions in a series circuit?

A

The current in each branch will only be identical if the resistance of the components along each branch are identical

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19
Q

why does current behave a certain way in a series circuit?

A
  • Electrons are physical matter – they cannot be created or destroyed
  • total number of electrons (and hence current) going around a circuit must remain the same
  • When the electrons reach a junction, however, some of them will go one way and the rest will go the other
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20
Q

How do you find the potential difference in series circuit?

A

several cells are connected together in series, their combined EMF is equal to the sum of their individual EMFs

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21
Q

How do you find potential difference in parallel circuits?

A
  • potential difference across each component connected in parallel is the same

This is the opposite of the current, which is different in each branch

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22
Q

what are the advantages of parallel circuits?

A
  • The components can be individually controlled, using their own switches
  • If one component stops working the others will continue to function
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23
Q

How are resistors in series circuit?

A

The combined resistance of the components is equal to the sum of individual resistances

24
Q

How are resistors in parallel circuits?

A

The combined resistance decreases and is less than the resistance of any of the individual components

25
Q

How do you determine the resistance in a parallel circuit?

A
  • 1/R = 1/R1 + 1 / R2
  • To calculate the resistance:
    First find the value of 1/R (by adding 1/R1 + 1/R2)
  • Next find the value of R by using the reciprocal button on your calculator (labelled either x-1 or 1/x, depending on your calculator)
26
Q

What does the potential difference across each resistor depend on?

A

Resistance

27
Q

What is a potentiometer?

A

single component that (in its simplest form) consists of a coil of wire with a sliding contact, midway along it

28
Q

What effect does the sliding contact have?

A

separating the potentiometer into two parts – an upper part and a lower part – both of which have different resistances

29
Q

What happens when 2 resistors are connected ins eries?

A

Kirchhoff’s Second Law, the potential difference across the power source is divided between them

30
Q

What are potential dividers?

A

circuits which produce an output voltage as a fraction of its input voltage

31
Q

What is the purpose of potential dividers?

A

produce an output voltage as a fraction of its input voltage

32
Q

What are potential dividers used for?

A
  • To provide a variable potential difference
  • To enable a specific potential difference to be chosen
  • To split the potential difference of a power source between two or more components
33
Q

What are potential divider circuits based on?

A

ratio of voltage between components. This is equal to the ratio of the resistances of the resistors

34
Q

What is the potential divider equation?

A

V out = R2 / R1 + R2 x V in

  • R2 is the numerator and the resistance of the resistor over Vout
  • R1 is the other resistance in series
  • Vout is the output potential difference
  • Vin is the input potential difference
35
Q

What is the second way to write the potential divider equation?

A

V out = R1 / R1 + R2 x V in

  • R1 is the numerator and the resistance of the resistor over Vout
  • R2 is the other resistance in series
36
Q

How is Vin and Vout measured?

A

input: input voltage Vin is applied to the top and bottom of the series resistors

Output: output voltage Vout is measured from the centre to the bottom of resistor R2

37
Q

How does the potential difference V across each resistor depend on its resistance R?

A
  • The resistor with the largest resistance will have a greater potential difference than the other one from V = IR
  • If the resistance of one of the resistors is increased, it will get a greater share of the potential difference, whilst the other resistor will get a smaller share
38
Q

What is p.d. across a component proportional to?

A

Resistance from V = IR

39
Q

What are the common hazards?

A
  1. damaged insulation
  2. overheating of cables
  3. Damp conditions
  4. excess current from overloading of plugs, single and multiple sockets when using a mains supply
40
Q

What is included in hazard of damaged insulation?

A

If someone touches an exposed piece of wire, they could be subjected to a lethal shock

41
Q

What is included in hazard of overheating of cables?

A

Passing too much current through too small a wire (or leaving a long length of wire tightly coiled) can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires

42
Q

What is included in hazard of damp conditions ?

A

If moisture comes into contact with live wires, the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk

43
Q

What is included in hazard of excess current from overloading of plugs, single and multiple sockets when using a mains supply ?

A

If plugs or sockets become overloaded due to plugging in too many components the heat created can cause fires

44
Q

What is mains electricity?

A

electricity generated by power stations and transported around the country through the National Grid

alternating current (a.c.) supply

45
Q

How is domestic supply energy in the UK?

A
  • frequency of 50 Hz and a potential difference of about 230 V
  • A frequency of 50 Hz means the direction of the current changes back and forth 50 times every second
46
Q

Does main electricity have a positive and negative side?

A
  • does not have positive and negative sides to the power source
  • The equivalent to positive and negative are called live and neutral and these form either end of the electrical circuit
47
Q

What are safety features built into domestic appliances?

A
  • Double insulation
  • Earthing
  • Fuses
  • Circuit breakers
48
Q

What is double insulation?

A
  • Insulation around the wires themselves
  • A non-metallic case that acts as a second layer of insulation
  • do not require an earth wire
49
Q

What is earthing and what does it pose?

A
  • Many electrical appliances have metal cases
  • live wire (inside the appliance) came into contact with the case, the case would become electrified and anyone who touched it would risk being electrocuted
50
Q

What happens if the earth wire is an additional safety wire that can reduce the risk?

A
  • The earth wire provides a low resistance path to the earth
  • It causes a surge of current in the earth wire and hence also in the live wire
  • The high current through the fuse causes it to melt and break
  • This cuts off the supply of electricity to the appliance, making it safe
51
Q

What is a fuse?

A

a safety device designed to cut off the flow of electricity to an appliance if the current becomes too large (due to a fault or a surge)

52
Q

What do fuses consist of?

A

glass cylinder which contains a thin metal wire

53
Q

What happens if current in wire becomes to large in a fuse?

A
  • The wire heats up and melts
  • This causes the wire to break, breaking the circuit and stopping the current
54
Q

What does a trip switch do?

A
  • When the current is too high the switch ‘trips’ (automatically flicks to the off position)
  • This stops current flowing in that circuit
55
Q

How do u choose which fuse to use?

A
  • Fuses come in a variety of sizes (typically 3A, 5A and 13A) - in order to select the right fuse for the job, you need to know how much current an appliance needs
  • If you know the power of the appliance (along with mains voltage), the current can be calculated using the equation:

Current = power / voltage

Physics - IGCSE (24 decks)

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