Electricity - Electrical Components

Question 1

What is the equation for Resistance?

Answer 1

R = V/I

Question 2

What is the equation for resistance in a series circuit

Answer 2

R total = R1 + R2

Question 3

What is the equation for total resistance in a parallel circuit

Answer 3

1/Rtotal = 1/R1 + 1/R2

Question 4

What are the two laws which can be used to derive the equations for resistance?

Answer 4

Ohm’s Law & Kirchhoff’s Laws

Question 5

What is an Electrical Cell?

Answer 5

• power supply for a circuit
• Lets current flow from the positive terminal to
the negative terminal through the circuit
• Creates a potential difference across itself by
supplying energy to charges

Question 6

What is a Resistor?

Answer 6

• Component of an electrical circuit that
restricts flow of current in a circuit
•The Voltage across a resistor is directly
proportional to the current I through a resistor

Question 7

What is a Bulb?

Answer 7

• component that transforms electrical energy
into light energy
• The brightness of the bulb depends on its
power, which has the unit of watts, W
• The equation for Power is P = VI, where P =
Power, V = Voltage and I = Current
• Some bulbs are non-ohmic, especially
filament bulbs, this means that they do not
obey ohms law, and that the voltage is not
directly proportional to the current.
• When a bulb is not following ohm’s law, its
resistance increases as the voltage increases
due to a rising heat increasing the resistance.

Question 8

What is an Ideal Diode? And how does it accomplish the fact of being ‘ideal’?

Answer 8

• An Ideal Diode is a Component that only
allows current in one direction
• It does this by having infinite resistance in
one direction, while having zero resistance in
the other.

Question 9

What is a Real Diode? How does it compare to a Ideal Diode?

Answer 9

• A real Diode is a diode that has a very small
resistance in the direction where it should let
the current through, but a very large
resistance in the opposite direction
• This is can lead to a very small amount of
current passing through the opposite
direction, but this current is negligible.
• However, this does not occur if a voltage
which exceeds the ‘breakdown voltage’ of the
diode, this leads to the resistance decreasing
sharply, and the current being able to pass
through the opposite direction easily.

Question 10

What is a Fuse?

Answer 10

• a fuse is a device that allows current to flow
while it is below a certain value
• If the current exceeds the rating of the fuse, it
will ‘blow’ which breaks the circuit and stops
the current flowing altogether
• It consists of a thin strip of metal, which if the
current is too high, it will melt and break the
circuit.

Question 11

How does a Circuit Breaker compare to a Fuse?

Answer 11

• A Circuit Breaker is a device which can be
used multiple times instead of just once.
• a Circuit breaker works by having a bimetallic
strip which bends when it gets too hot,
causing a spring mechanism to get released
and break the circuit.
• can be used for smaller things, such as
household appliances, but can be also used
in large scale for things like high voltage
circuits that supply cities with power.

Question 12

What are Residual Current Devices?

Answer 12

• Residual Current Devices (RCDs) compare the
current in the live wire with that in a neutral
wire.
• They disconnect the circuit if there is a
difference of more than a few tens of
milliamps.
• It disconnects as a difference of more than a
few tens of milliamps can indicate a fault has
occurred and not all of the charge is returning
to the supply in a safe manner.

Question 13

What are RCBOs?

Answer 13

•RCBOs are circuit breakers which contain an
MCB to guard against faults causing too much
current and also an RCD to protect against
earthing faults

Question 14

What is a Thermistor?

Answer 14

• A thermistor is a device that decreases resistance as temperature increases.
• The resistance does not decrease linearly

Question 15

What is a transformer?

Answer 15

• A transformer is an electrical component that can step up or step down an alternate voltage
• An ideal transformer has 100% efficiency, which means that all the electrical power which goes in also comes out, and no heat is generated.
• the formula relating the number of turns of wire on the primary coil and the number of turns on the secondary coil to the voltages at the primary and secondary coils is given by:
Vp/Vs = Np/Ns

Question 16

What is an Ammeter?

Answer 16

• An Ammeter is a device that measures current flowing through it
• An ideal Ammeter has zero resistance, while real ammeters tend to have very low, often negligible resistance which allows the ammeter to be placed in series in a circuit without affecting the other parts of the circuit

Question 17

What is a Voltmeter?

Answer 17

• A voltmeter is a device that measures the potential difference between its end.
• An ideal Voltmeter has infinite resistance, such that no current flows through it.
• A real Voltmeter, has a very large resister, such that a very small or negligible current flows through it.

Question 18

What is a Capacitor?

Answer 18

• A capacitor is a component that consists of two conducting plates separated by an insulator
• It is used to temporarily store electrical charge and energy.
• The potential between the plates is always proportional to the charge separation.
• The equation for the capacitor value is C = Q/V