Topic 10 - Electricity and Circuits Flashcards
SP10a - Describe the structure of an atom including features of the sub-atomic particles.
- 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)
SP10a - Descirbe what a potential difference is.
The force that pushes the electrons to flow around the circuit.
SP10a - What is conventional current?
What we refer to as the direciton of current form positive to negative. Opposite to the flow of electrons.
SP10a - What are the two types of circuits?
- Series: everything connected in one route
- Parallel: many options for different routes.
SP10a - Why may parallel circuits be more beneficial?
- 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
SP10b - What is the unit for current and how can it be measured?
Amps (Amperes). Measured using an ammeter which is attached in series to the circuit
SP10b - What is the unit for potential difference and how can it be measured?
Volts. Measured using a voltmeter which is attached in parallel to the component you are measuring the potential difference of.
SP10b - How does total current differ in parallel and series circuits?
- 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.
SP10b - How does potential difference differ in parallel and series circuits?
- 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
SP10c - What is current?
- The flow of electrons
- The rate of flow of charge
SP10c - What is the unit for charge?
C - Coulombs
SP10c - What is the equation linking charge and current?
Q = I x t
(Charge = Current x time)
SP10c - What equation links energy and charge and how can this be changed to link energy to current?
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)
SP10d - What is Ohm’s law?
V = I x R
(p.d (V) = Current (A) x Resistance (Ω))
SP10d - What is resistance?
The force pushing back against p.d opposing and reducing the current.
SP10d - How do you calculate the resistance in series and parallel circuits?
- Series: Add up the resistance of all the components
- Parallel: 1/RT = 1/R1 + 1/R2 + ………..
SP10d - What is key to remember about the size of the total resistance in series and parallel and series circuits?
- S: It is greater than any of the individual resistances
- P: It is smaller than all of the individual resistances
SP10e - What does a IV graph for fixed resistor look like and why?
- It is a straight diagonal line showing direct proportion.
- This is because resistors are ohmic conductors.
- The voltage is directly proportionate to the current.
SP10e - What is an ohmic conductor?
A component in a circuit that follows Ohm’s rule of V=IxR
SP10e - What does the gradient of an IV graph represent?
The inverse of the resistance (1/R)
SP10e - What does a IV graph for diode look like and why?
- 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
SP10e - What does a IV graph for filament lamp look like and why?
- 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
SP10e - Describe what a graph for resistance of a thermistor would look like and why.
- 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.
SP10e - Describe what a graph for resistance of an LDR (Light-dependant resistor) would look like and why.
- 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
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.
- 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
SP10f - What is the heating effect?
- 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
SP10f - Where is the heating effect useful?
- 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.
SP10f - Describe what resistance is in terms of a metal’s structure.
- 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
SP10f - How can resistance be reduced in a circuit?
- 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)
SP10f - What formula links energy, time and voltage?
E = I x t x V
Energy = Current x time x Voltage
SP10g - What are the four formulae for power?
- P = E/t
- P = I x V
- P = I² x R
- P = V² ÷ R
SP10g - How do you form the the equations that link Power and Resistance?
- 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
SP10h - What the voltage and frequency of and type of electricity that comes through mains supply?
- 230V
- 50Hz (changes diretion 50 times per second)
- a.c
SP10h - What are the differences between d.c and a.c?
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
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SP10i - Describe the five features of a 3-pin plug.
- 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
SP10i - How does an earth wire make an appliance safer?
- 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
SP10i - How does a fuse provide safety? (Describe this though it’s structure)
- 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
SP10i - How do you choose the best value for a fuse?
- 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
SP10i - What are circuit breakers and how do they work?
- Circuit breakers are automatic swtiches that detect a rise in current and automatically switch off the supply safely.
- They are an alternate to fuses.
SP10i - Why are circuit breakers more advantageous than fuses?
- 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
SP10i - What are the colours of the earth, neutral and live wires?
- Earth wire: Green and yellow
- Neutral wire: Blue
- Live wire: Brown
SP10i - Why may fuses be more advantageous than circuit breakers?
- Fuses are cheaper
- More practical for small scale uses (e.g. small appliances)
