Topic 10 - Electricity and Circuits

Question 1

SP10a - Describe the structure of an atom including features of the sub-atomic particles.

Answer 1

• Proton and neutron in the nucelus, each with a relative mass of 1.
• Protons have a charge of +1.
• Electrons orbit in energy levels each with a charge of -1 and a relative mass of 1/1835 (negligible)

Question 2

SP10a - Descirbe what a potential difference is.

Answer 2

The force that pushes the electrons to flow around the circuit.

Question 3

SP10a - What is conventional current?

Answer 3

What we refer to as the direciton of current form positive to negative. Opposite to the flow of electrons.

Question 4

SP10a - What are the two types of circuits?

Answer 4

• Series: everything connected in one route
• Parallel: many options for different routes.

Question 5

SP10a - Why may parallel circuits be more beneficial?

Answer 5

• If the circuit becomes incomplete along one path, the rest of the circuit can still continue to function. (e.g - Switches can be connected to different parts meaning lights in parallel to each other can be switched in and off individually)
• If a bulb goes off, the rest of the circuit in parallel to this can still continue to function

Question 6

SP10b - What is the unit for current and how can it be measured?

Answer 6

Amps (Amperes). Measured using an ammeter which is attached in series to the circuit

Question 7

SP10b - What is the unit for potential difference and how can it be measured?

Answer 7

Volts. Measured using a voltmeter which is attached in parallel to the component you are measuring the potential difference of.

Question 8

SP10b - How does total current differ in parallel and series circuits?

Answer 8

• S: The total current is the same at all points throughout the circuit
• P: The total current gets split between the branches of the circuit, inversely proportionate to the resistance of the components in those branches.

Question 9

SP10b - How does potential difference differ in parallel and series circuits?

Answer 9

• S: The p.d is different across different components, directly proportionate to the resistance of that component
• P: The p.d is tha same at all points across the circuit

Question 10

SP10c - What is current?

Answer 10

• The flow of electrons
• The rate of flow of charge

Question 11

SP10c - What is the unit for charge?

Answer 11

C - Coulombs

Question 12

SP10c - What is the equation linking charge and current?

Answer 12

Q = I x t

(Charge = Current x time)

Question 13

SP10c - What equation links energy and charge and how can this be changed to link energy to current?

Answer 13

E = Q x V (Energy = Charge x p.d)

since Q = I x t, this means that

E = I x t x V (Energy = Current x time x p.d)

Question 14

SP10d - What is Ohm’s law?

Answer 14

V = I x R

(p.d (V) = Current (A) x Resistance (Ω))

Question 15

SP10d - What is resistance?

Answer 15

The force pushing back against p.d opposing and reducing the current.

Question 16

SP10d - How do you calculate the resistance in series and parallel circuits?

Answer 16

• Series: Add up the resistance of all the components
• Parallel: 1/R_T = 1/R₁ + 1/R₂ + ………..

Question 17

SP10d - What is key to remember about the size of the total resistance in series and parallel and series circuits?

Answer 17

• S: It is greater than any of the individual resistances
• P: It is smaller than all of the individual resistances

Question 18

SP10e - What does a IV graph for fixed resistor look like and why?

Answer 18

• It is a straight diagonal line showing direct proportion.
• This is because resistors are ohmic conductors.
• The voltage is directly proportionate to the current.

Question 19

SP10e - What is an ohmic conductor?

Answer 19

A component in a circuit that follows Ohm’s rule of V=IxR

Question 20

SP10e - What does the gradient of an IV graph represent?

Answer 20

The inverse of the resistance (1/R)

Question 21

SP10e - What does a IV graph for diode look like and why?

Answer 21

• A line that is nearly on the x-axis till it shoots up.
• This is because a diode has an infinitely high resistance till a point where it has an infinitely low resistance

Question 22

SP10e - What does a IV graph for filament lamp look like and why?

Answer 22

• An S shaped ‘curve’.
• This is because the resistance of a lamp increases due to the temperature increase as it conducts electricity at a higher voltage

Question 23

SP10e - Describe what a graph for resistance of a thermistor would look like and why.

Answer 23

• The x-axis would be temperature (°C) and the y-axis would be resistance (Ω)
• As the temperature increases, the resistance decreases. This forms a negative curve in an L shape
• This can be used to reduce the current in lower temperatures.

Question 24

SP10e - Describe what a graph for resistance of an LDR (Light-dependant resistor) would look like and why.

Answer 24

• The x-axis would be light intensity (lux) and the y-axis would be resistance (Ω)
• As the light intensity increases, the resistance decreases. This forms a negative curve in an L shape
• This is used for lit up signs outside. In darker conditions (lower light intensity) bulbs don’t need to be as bright.
• Thus, the resistance is higher to reduce the current and brightness
• Resistance is high against the dark side #Starwars

Question 25

SP10e CP - Describe your set-up for an experiment to compare the relationship of V=IxR in a resistor, and a filament lamp in parallel/series.

Answer 25

• Set up a series circuit with a power pack, an ammeter, a fixed resistor and a voltmeter in parallel to this.
• Provide different voltages from the power pack.
• For each voltage provided, note down the current - Replace the fixed resistor with a lamp and repeat
• Set up the circuit from here so that there is a voltmeter attached in parallel to this.
• Attach another lamp to the circuit with another voltmeter in parallel to this
• Measure out the voltages and currents when different voltages are supplied
• Move one of the bulbs with its voltmeter to a new branch forming a parallel circuit
• Add an ammeter to each branch of the circuit
• Now measure the voltage and current depending on the voltage provided

Question 26

SP10f - What is the heating effect?

Answer 26

• The heating effect is when a circuit warms up due to the resistance in its wires.
• Work is done against the resistance and so energy is transferred.
• This is in the form of heating and dissipates into the surroundings

Question 27

SP10f - Where is the heating effect useful?

Answer 27

• In appliances such as electric heaters and kettles where the aim is to use thermal energy, the heating effect is incredibly useful.
• In these circuits, resistance tends to be high.

Question 28

SP10f - Describe what resistance is in terms of a metal’s structure.

Answer 28

• Current is the flow of electrons.
• A metal is made of electrons flowing around positive metal ions
• When the electrons are moving in the circuit, they can collide into these posistive metal ions.
• These collisions are resistance and they transfer energy

Question 29

SP10f - How can resistance be reduced in a circuit?

Answer 29

• Choosing a metal with a lower resistance
• Using a thicker wire (more space for electrons to flow)
• Using a shorter wire (less distance in which they can collide)

Question 30

SP10f - What formula links energy, time and voltage?

Answer 30

E = I x t x V

Energy = Current x time x Voltage

Question 31

SP10g - What are the four formulae for power?

Answer 31

• P = E/t
• P = I x V
• P = I² x R
• P = V² ÷ R

Question 32

SP10g - How do you form the the equations that link Power and Resistance?

Answer 32

• We know that P = I x V and that V = I x R
• If we substitue the V in the first equation we get P = I x I x R or P = I² x R
• If we rearrange V = I x R we get I = V ÷ R
• So if we substitute this in we get P = V x V ÷ I or P = V² ÷ R

Question 33

SP10h - What the voltage and frequency of and type of electricity that comes through mains supply?

Answer 33

• 230V
• 50Hz (changes diretion 50 times per second)
• a.c

Question 34

SP10h - What are the differences between d.c and a.c?

Answer 34

d.c:

• Only one direction (positive to negative)
• Electrons loose energy as they travel from positive to negative
• A grpah showing the direction will only ever be on one side of the x-axis

a.c:

• Constantly switching direction (this is their frequency)
• Electrons vibrate and pass on energy
• A graph showing direction will contantly cross zero and over the x-axis

_{A̶C̶/̶D̶C̶ ̶a̶r̶e̶ ̶a̶n̶ ̶A̶u̶s̶t̶r̶a̶l̶i̶a̶n̶ ̶r̶o̶c̶k̶ ̶b̶a̶n̶d̶ ̶f̶o̶r̶m̶e̶d̶ ̶i̶n̶ ̶S̶y̶d̶n̶e̶y̶ ̶i̶n̶ ̶1̶9̶7̶3̶ ̶b̶y̶ ̶b̶r̶o̶t̶h̶e̶r̶s̶ ̶M̶a̶l̶c̶o̶l̶m̶ ̶a̶n̶d̶ ̶A̶n̶g̶u̶s̶ ̶Y̶o̶u̶n̶g̶.̶}

Question 35

SP10i - Describe the five features of a 3-pin plug.

Answer 35

• Live wire: Connects the appliance to the generators at the power station providing 230V
• Neutral wire: The return path to the power station and will be at 0V if circuit is correctly connected
• Earth wire: Connects the metal parts of the appliance to a large spike of metal that pushes down and connects to the ground. Will be at 0V unless the circuit is incorrectly connected
• Fuse: A Safety device usually 3, 5 or 13 A
• Plastic casing: This electrical insulator allows you to safely hold the plug

Question 36

SP10i - How does an earth wire make an appliance safer?

Answer 36

• If a wire comes loose and touches the metal part of the appliance, the electricity will beable to flow through this.
• When a person touches it, the electricity can pass through the person to the ground.
• This would give them an electric shock.
• However the earth wire provides an easier way to travel to the ground.
• As electrcity always takes the past of least resistance, it goes this way and the person doesn’t get an electric shock

Question 37

SP10i - How does a fuse provide safety? (Describe this though it’s structure)

Answer 37

• A fuse is a glass tubing with a thin metal wiring that the electricity passes through.
• A faulty appliance may draw too much current which would heat up and cause a fire.
• However depending on the value of the fuse, it will melt once the current has reached a certain level and cause the circuit to be incomplete meaning current stops flowing through it

Question 38

SP10i - How do you choose the best value for a fuse?

Answer 38

• Fuses are typically found in 3A, 5A, and 13A.
• You want to pick one that has a current higher than what the current of the appliance is but not to high.
• This way it will stop a fualty appliance but not a properly functioning one.
• If an appliance has a current of 3A, you would pick a 5A fuse. 3A would be too low and 13A would be too high

Question 39

SP10i - What are circuit breakers and how do they work?

Answer 39

• Circuit breakers are automatic swtiches that detect a rise in current and automatically switch off the supply safely.
• They are an alternate to fuses.

Question 40

SP10i - Why are circuit breakers more advantageous than fuses?

Answer 40

• They can just be turned back on rather than having to buy a new fuse
• They work quicker.
• You elliminate the risk of an accident occuring while the fuse is melting

Question 41

SP10i - What are the colours of the earth, neutral and live wires?

Answer 41

• Earth wire: Green and yellow
• Neutral wire: Blue
• Live wire: Brown

Question 42

SP10i - Why may fuses be more advantageous than circuit breakers?

Answer 42

• Fuses are cheaper
• More practical for small scale uses (e.g. small appliances)