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Physics - Lizzie > Current Electricity > Flashcards

Current Electricity Flashcards

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1
Q

What is the symbol for time, the unit and the symbol for the unit?

A

Symbol - t
Unit - second
Symbol for seconds - s

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2
Q

What is the symbol for current, the unit and the symbol for the unit?

A

Symbol - I
Unit - Amp
Symbol for Amps - A

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3
Q

What is the symbol for energy, the unit and the symbol for the unit?

A

Symbol - E
Unit - joule
Symbol for joules - J

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4
Q

What is the symbol for voltage, the unit and the symbol for the unit?

A

Symbol - V
Unit - volt
Symbol for volts - v

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5
Q

What is the symbol for resistance, the unit and the symbol for the unit?

A

Symbol - R
Unit - omh
Symbol for ohms - Ω

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6
Q

What is the symbol for power, the unit and the symbol for the unit?

A

Symbol - P
Unit - joules per second/watt
Symbol for units - J/s / W

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7
Q

What equation links current, charge and time?

A

I = Q/t

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8
Q

What equation links energy, voltage and charge?

A

V = E/Q

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9
Q

What equation links voltage, current and resistance?

A

R = V/I

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10
Q

What equation links power, energy transferred and time?

A

t = e.t./P

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11
Q

What equation links power, voltage and current?

A

V = P/I

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12
Q

Voltage is low ->

A

current is low -> temperature is low -> resistance of the filament is low
• Gradient is high

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13
Q

Voltage is high ->

A

current it high -> temperature is high -> resistance of the filament is high
• Gradient is low

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14
Q

What is the symbol for charge, the unit and the symbol for the unit?

A

Symbol - Q
Unit - coulombs
Symbol for coulombs - C

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15
Q

How to find out resistance when voltage is proportional to current and the gradient is known?

A

Resistance = 1/gradient

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16
Q

Rules for current and voltage in a series circuit

A
  • Current doesn’t change in a series circuit.
  • In series, voltage is shared between all components.
  • In parallel, voltage is the same with each branch of the circuit.
17
Q

What is charge measured in?

A

Charge = Q

Measured in Coloumbs (C)

18
Q

What is a thermistor and how does its resistance change?

A
  • Thermistors can detect and sense temperatures.

* As the temperature increases, the resistance decreases.

19
Q

What is an LDR and how does its resistance change?

A
  • Light dependent resistors can detect light levels.

* As light intensity increases, their resistance decreases.

20
Q

Where do you put an ammeter in a circuit?

A

• Anywhere in the main circuit in series, but not in parallel.

21
Q

Where do you put the voltmeter?

A
  • In parallel, across the component.

* Not around the variable resistor or battery!!!

22
Q

What are alternating (ac) and direct (dc) currents?

A
  • Alternating currents are constantly changing direction - mains electricity is an ac supply.
  • Direct current are always the same direction - cells and batteries supply direct current.
23
Q

Recipe for a safe plug:

A
  • Firmly screw in the rightly coloured wire to its corresponding pin.
  • No bare wires inside the plug.
  • Fasten the cable grip tightly over the cable outer layer.
  • Metal parts are made of copper or brass (good conductors).
  • Case, cable grip and cable insulation are made of flexible rubber or plastic (good insulators).
24
Q

How does the earth wire work?

A
  • Live wire manages to touch the metal case.
  • The case is earthed, so a large current flows through the live.
  • The current then flows through the case and out down the earth wire.
  • The surge of current causes the fuse to melt (or the circuit breaker to be tripped) and cuts off the live supply.
  • The appliance cannot get electricity - no chance of an electric shock or fire from overheating.
25
Q

What does it mean to double insulate an appliance?

A
  • If an appliance has a casing made out of plastic (instead of metal - which conducts electricity making electric shocks possibles) and has no metal parts showing, it is double insulated.
  • If an appliance is double insulated, it doesn’t require an earth wire.
26
Q

How do fuses work?

A
  • Fuses contain a thin piece of wire which has a low melting point.
  • If there is a current which is too large flowing in the circuit, the fuse wire will become very hot and melt.
  • If the fuse has melted (‘blown’), the circuit is shut off and you cannot get an electric shock or have an electrical fire.
27
Q

How do circuit breakers work?

A
  • Very similar to fuses.
  • If a circuit breaker detects a surge in the current, it will break the circuit by opening a switch.
  • To reset them, one flicks a switch on the device (more convenient than fuses, as once a fuse melts it has to be replaced).
28
Q

Why is it bad to have water near electrical objects?

A

Water is a very good conductor, so the current would pass through it and cause an electric shock.

29
Q

What are the different types of fuses?

A

• 3A, 5A and 13A.

30
Q

Why do some appliances have thick cables?

A
  • Thick cables have a lower resistance.
  • Thick cables are easy to insulate.
  • Thick cables produce less heat.
31
Q

What is voltage?

A

The amount of energy transferred per unit of charge (Coulomb). 1 Volt = 1 Joule/Coulomb.

32
Q

What is current?

A

The rate of flow of charge.

33
Q

Why might a series circuit be more appropriate for a particular application?

A
  • In a series circuit the voltage is shared out between all the components and therefore might be useful to supply low power things, such as fairy lights.
  • In a series there are fewer wires used.
  • In a series the resistance values are lower.
34
Q

Why might a parallel circuit be more appropriate for a particular application?

A
  • In a parallel circuit, each component receives full voltage, so it is useful for supplying power to high energy things.
  • It might be more practical because if component in the circuit breaks, the rest of the circuit will still work because the different components are connected separately to the supply.
35
Q

A kitchen has a water supply, an electricity supply and electric lighting. There is a toaster, a kettle, a clothes iron, a microwave oven and a dishwasher.
What are the hazards of electricity in this kitchen?

A
  • Electrical devices with heating elements (e.g. the kettle) can reach high temperatures, which can cause (skin) burns and fires (if the insulation melts).
  • Electricity coming into contact with water is hazardous (e.g. dishwasher) because water conducts electricity and can therefore cause an electric shock.
  • Damaged equipment can cause many hazards, such as a fault microwave leaking cancer-causing microwaves. Live parts must not be exposed which could lead to electric shocks.
  • With many electrical appliances, there is a danger of the sockets being overloaded (which can cause a fire). Circuit must have correct fuses and there must be sufficient sockets.
  • Having many electrical appliances means there is a trip hazard of all the cables. Short leads could be used to reduce the hazard.
  • There is a danger of sticking metal objects into sockets/heating elements which can cause an electric shock. Sockets could be covered to stop people being able to put things in them and tools must be insulated properly.
36
Q

What does a variable resistor do?

A

It enables someone to control the current in a circuit.

37
Q

Why would you want to keep the temperature of a wire constant when working out the difference in resistance by changing voltage?

A
  • Resistance changes with temperature.
  • A hot wire would be dangerous as it might melt or catch fire.
  • Voltage is only proportional to current at a constant temperature.
  • Ohm’s law is only true if the temperature is constant.

Physics - Lizzie (19 decks)

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