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gcse physics (aqa) > Topic 2: Electricity (Paper 1) > Flashcards

Topic 2: Electricity (Paper 1) Flashcards

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1
Q

~ Current ~
* What is an electric current?
* What is the unit of electric current?
* How can we measure the current in a circuit?
* How will current be addected if we put this component in another position?
* Wht direction does the electric current flow?

A
  • The flow of electric charge around a circuit.
  • ampere (A) / amps
  • by using an ammeter
  • current is never used up in a circuit, in series the current will be the same all the way around
  • negative end of the cell to the positive end
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2
Q

~ Current ~
* How do lamps light up in a circuit?
* What direction is the convectional current?

A

~ Current~
* electrons carrt energy from the cell to the lamp, electrons pass this energy to the components in the circuit (e.g. the lamp), electrical energy transferred to light and thermal energy
* postitive to negative end of the cell

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3
Q

~ Series and Parallel~
* How can you know that a circuit is a series circuit?
* How do you know that a circuit is a parallel circuit?
* How is the current affected when the ammeter is placed in a different position in a parallel circuit?
* What is key about the current in a parallel circuit?

A
  • no branches, current only flows in one path
  • circuit contains branches
  • current splits when passing through branches, different current in each branch
  • the current in each branch adds up to the totak current leaving the cell
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4
Q

~ Potential Difference ~
* What does a potential difference of 1V tell us?
* How do we measure the potential difference in a circuit?
* Where does a voltmeter have to be placed in the circuit?
* How does the potential difference in a circuit differ when we move the voltmeter’s position, in a series circuit

A
  • a potential difference of 1V tells us that 1J of energy is transferred for each coulomb of charge that is moving through the circuit
  • We can measure potential difference in a circuit using a voltmeter
  • has to be placed in parallel to a circuit
  • potential difference is the same everywhere in the circuit
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5
Q

~ Potential difference ~
* What does the constant potential difference show?
* What happens to the brightness of one lamp, if we add another lamp to the same circuit, in series?
* How is the potential difference divided by two lamps instead on one?
* What is the total potential difference across both lamps compared to the cells?

A
  • that all the electrical energy is transferred into other forms of energy when passing through components
  • lamp 1 becomes dimmer than how it was before the new lamp was added.
  • the total energy carries by the electric current has been shared between the two lamps
  • the total potential difference across both lamps is equal to the potential difference across the cell
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6
Q

~ Potential Difference ~
* Why would a lamp with 6V be brighter than a lamp with 3V?
* How does the potential differece differ when we move the position of the voltmeter, in a parallel ciruit?

A
  • the 6V lamp is transferring more energy so it is brighter (6J per coulomb od charge)
  • for components connected in parallel the potential diffrence across each component is the same
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7
Q

~ Batteries ~
* What is a battery?
* How must cells in a battery be connected?

A
  • 2 or more cells connected together
  • they must both be facing in the same direction
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8
Q

~ Charge ~
* What is electrical charge measured in?
* What does a current of 1A tell us?
* What is the equation for electrical charge?
* What equation can we use to calculate the energy transfrred bu using the charge we have just worked out?

A
  • Coulombus, C
  • a current of 1A = 1C per second
  • charge (C) = current (A) x time (s)
  • energy (J) = charge (C) x potential difference (V)
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9
Q

~ Resistance ~
* What is resistance?
* What does a lower potential difference of one lamp tell us?
* What is the equation for resistance?
* How can a resistor be useful?

A
  • when they move, electrons collide with atoms in the metal, transferred electrical energy into other forms (e.g. thermal), resistance tells us the potential differece required to drive a current through a component
  • less potential difference to drice the current through the lamp - lower resistance
  • potentail diffrence (V) = current (A) x resitance (Ohms/Ω)
  • resistor increases resistance in a ciruit, reduce current, less potential difference accross component, lamp is dimmer, LED dosen’t get destroyed
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10
Q

~ Potential diffrence and current ~
* What is the relationship between the current through a resistor and the potential difference?
* What would happen to the potential difference if we increase the current?

A
  • current is directly proportional to potential difference
  • if we increase the current, the potential difference will also increase
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11
Q

~ I-V characterisitcs ~
* What is an ohmic conductors?
* What must stay the same, for an ohmic conductor?
* What is a filament bulb?
* How does a filament lamp work?
* Why is the current through a filament lamp not directly proportional to the potential difference?

A
  • A resistor in which the current is directly proportional to the potential difference.
  • A constant temperature
  • Very tightly coiled wire
  • Wire gets extremely hot when electric current passes through, causes wire to glow, gives out light
  • current is directly proportional to portential difference only if the temperature is constant, filament gets how when electric current passes through which causes the resistance to increase, at high temperatures, the atoms vibrate more, electrons collide more eith atoms, more energy is needed to push the current through the filament
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12
Q

~ I-V Charateristics ~
* What does the I-V graph for a filament lamp look like?
* What does a diode do?
* How does a diode do this?
* What does the I-V graph for a diode look like?
* What does this graph shlow?

A
  • it is in an ‘s’ shape
  • allows current to flow in one direction only, controls the flow of current in circuits
  • has a very high resistance in the reverse direction
  • curve only in the positive part of the graph, negatice side shows that there is no current in the reverse direction, postivie side (steeper gradient) shows that there is a current in the foward direction
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13
Q

~ LEDs ~
* What does the LED stand for?
* What does an LED do?
* Why are LEDs useful?

A
  • Light emitting diode
  • emits light when a current flows through
  • LEDs are an extremely energy-efficient source of light
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14
Q

~ Resistance ~
* What is the resistance of 2 resistors are in series and why?
* What is equivalent resistance?
* What is the total resistance of 2 resistors if they are connected in parallel?
* Why is the total resistance when resistors are connected in parallel different to the total resitance in series?

A
  • the resistance from resistors in series add together (current has to pass through each resistor in turn and cannot bypass any resistor)
  • when we replace 2 or more resistors with a single resitor and get the same resistance
  • total resistance < resistance of the smallest individual resistor
  • in parallel, there are 2 or more pathways for the current tp take, more total current will flow through the circuit; if current has increased but the potential diffrence hasn’t changed, then the total resistance must have decreased
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15
Q

~ LDRs ~
* What does LDR stand for?
* What happens to the resistance of an LDR if there is minimal light, vice versa?
* Why can the current easily pass through an LDR in the light and what does this mean for the potential difference?
* Why does a lamp in series to an LDR turn on in light conditions?

A
  • Light-dependent resistor
  • in dark conditions, the LDR has a high resistance, in light conditions the resistance is very low
  • in the light, resistance of an LDR is high so low energy needed for the current to pass through, potential difference will be very low because the potential difference us energy per coulomb of charge
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16
Q

~ LDRs ~
* Why does a lamp in series to an LDR turn on in light conditions?
* Why does the lamp turn off in dark conditions?

A
  • potential difference is shared between components in series to equal the potential diffrenece across the cell, potential difference is low across the LDR so the potential difference has to be high across the lamp, high potential difference = high amount of energy passing through so it is bright
  • in dark conditiond, resistance of the LDR is very high, takes a lot of energy for the current to pass through the LDR, high energy = high potential difference in LDR, potential differece is shared between components in series to equal potential difference across initial cell, potential difference across LDR is very high, potential difference across lamp has to be low, low potential difference = low energy - dim
17
Q

~ Thermistors ~
* What happens to the resistance of a thermistor if the temperature increases?
* How does a cooling fan with a thermistor cool a computer down?
* What are the other uses of a thermistor?

A
  • resistance is inversly proportional to temperature, if temperature increases resistance descreases
  • if a computer gets too hot (temperature increases) the resistance of the thermistor decreases, dosen’t take much energy for the current to pass through the thermistor, so a low potential difference, potential difference is shared across components in series in order to equal the potential difference at the cell, low potential difference across thermistor, means a high potential difference across cooling pan, more energy, operates at a higher speed, cools computer down
  • incubators (fall in temperature detected by thermistor sounding an alarm), thermostats
18
Q

~ Required Practical ~
Describe a method to investigate the factors that affect resistance?

A

1) Attach a wire to a metre ruler using tape.
2) Connect 10cm of the wire into the rest of the circuit using crocodile clips.
3) Measure and record the potential difference of the wire (using a voltmeter) as well as the current of the circuit (using an ammeter).
4) Repeat for 20cm, 30cm, etc up to 100cm.
4) Calculate the resistance of the wire using R = V/I
5) Plot a graph of the resistance against the length of wire.

resistance is proportional (∝) to the length of the wire

19
Q

~ Required Practical ~
* What are some of the possible issues with this experiment?
* What is a potential hazard for the ‘resistance of a wire’ required practtical, and how can we prevent this hazard?

A
  • zero error; (reading when the value should be zero) there is some resistance when wire = 0m (croc clip is not exactly at 0m & some resistance caused by the contact between the croc clip and the wire) OR if the temperature of the wire increases, then the resistance of the wire will also increase => use a low potential difference OR only turn on the current when taking a reading
  • hazard = high current: may cause wire to melt / overheat, may cause burns (to skin) –> use low currents
20
Q

~ Required Practical ~
* How can we investigate current and potential difference characteristics using a resistor?
* Why is it important that we don’t leave this circuit on for too long?

A
  • circuit with ammeter in series
  • voltmeter in parallel to resistor
  • resistor is series with a variable resistor

1) Use the voltmeter to read the potential difference across resistor.
2) Use the ammeter to read the current throguh the resistor.
3) Record these values in a table.
4) Adjust the variable resistor and record the new readings on the voltmeter and ammeter.
5) Switch the direction of the battery to get the negative values.
6) Plot a graph of the current against the potential difference.

=> current through resistor is directly proportional to the p.d.
=> resistor = ohmic conductor

  • temperature will increase - affects the resistance
21
Q

~ Required Practical ~
* How can we investigate current and potential difference characteristics using a filament lamp?

A
  • same circuit but with a filament lamp instead of the resistor

1) Read the values for the potential difference and current using the voltmeter and ammeter.
2) Adjust the variable resistor and take several readings.
3) Repeat again but with battery in the reverse direction to get negative values.
4) Plot a graph

=> filament lamp’s I/V graph is not a straight line through zero => filament lamp is not an ohmic conductor

22
Q

~ Required Practical ~
* How can we investigate current and potential difference characteristics using a diode?
* Why do we use an extra resistor?
* What would the graph look like for the diode experiment? Why do we get a graph like this?

A

1) Adjust the variable resistor several times and record the potential difference and current.
2) Repeat for reverse direction.
3) Plot a graph.

-same circuit but instead of the filament lamp, a diode is used
- extra resistor is also connected in series because dioes are very easily damaged by a high current (so we need a milliammeter)
- no current in reverse direction
(diode only allows current to flow in one direction) because it has a high resistance

23
Q

~ Power ~
* What is power?
* What is the equation for energy transferred using power?
* What is the equation for power, using resistance and current?
* What is the equation for power using potential difference and current

A
  • power (W) = the rate at which energy is transferred
  • P = V x I : power (W) = p.d. (V) x current (A)
  • P = I² x R :power = (current)² x resistance (Ω)
24
Q

~ A.C. and D.C. ~
* What type of current is produced by a battery?
* What direction does the current in a battery flow?
* What type of current is produced by mains electricity in the UK?
* What direction does the mains electircity flow?
* What is the main benefit of using an AC?

A
  • direct current - DC
  • only in one direction, from one end of the cell, around the circuit too the other
  • alternating current - AC
  • the altenating current is always changing direction
  • alatternating currents make it easy to se a transformer to increase/decrease the potential difference
25
Q

~ A.C. and D.C. ~
* What frequency does the AC have in the UK?
* What potential difference does the AC have in the UK?
* What would an AC look like on an oscilloscope?
* What would a DC look like on an oscilloscope?

A
  • frequency of 50Hz
  • potential difference of 230V
  • transverse wave, p.d. rising and falling, maximum peak at 230V
  • straight, horizontal line at 230V
26
Q

~ Plugs ~
* What is the three-core cable?
* What is the brown wire called? What is the purpose of it? What p.d. does it carry?
* What is the blue wire called? What is the purpose of it What p.d. does it carry?
* What is the green/yellow striped wire called? What is the purpose of it?
* Describe the circuit diagram with the 3 wires.

A
  • three copper wires (good conductorof electricity) plastic coatings around wire (insulator which does not conduct electricity)
  • live wire - carries the alternating p.d. from the supply (230V)
  • neutral wire - completes the circuit, carries a p.d. of 0V
  • earth wire - safety wire to stop te appliance from becoming live
    • brown live wire carries 230V electricity from generators, energy then transferred in the appliance blue neutral wire completes the circuit
27
Q

~ Plugs ~
* What would happen if someone touched the live wire?
* Why may an appliance with a metal case be dangerous?
* How does the earth wire prevent an appliance from becoming live?

A
  • current would flow through the person into the earth => electrocution
  • if the live wire becomes loose and touches the metal case, the case can become live (has 230V) => fatal electric shock if touch
  • metal case is attached to the live wire, earth wire connected into the ground with a metal rod
    => if metal case does become live, the current flows to the earth, the fuse melts and shuts off the current
28
Q

~ The National Grid ~

A

gcse physics (aqa) (2 decks)

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