09 Circuits and Mains Electricity Flashcards
Why would an appliance NOT need an Earth wire?
It is double insulated
It has a plastic casing OR the electrical components are incased by plastic
Why are the bulbs dimmer in the second circuit?
Voltage is shared between bulbs in series
Less voltage across each bulb therefore bulb is dimmer.
Adding second bulb in series, doubles the resistance of the circuit, halving the current as well - bulbs are dimmer for this reason as well.
Define voltage
Energy per unit charge either supplied by a cell, or transferred to a component.
What component symbol is shown below?
Light dependent resistor
What type of current is shown in the image?
Alternating current
Current that constantly changes direction
i.e. 50 Hz or 50 times a second
What is voltage measured in?
Volts or V
What is the voltage across a cell or power supply a measure of?
The energy transferred from chemical store electrically to the wires per coulomb
What component symbol is shown below?
bulb
What component symbol is shown below?
ammeter
Define current
- The rate of flow of charge
OR
- the number of coulombs passing a point in a circuit per unit time
(It is not the speed of the electrons!)
Which wire is circled in the image?
Earth wire
What happens to the total resistance and current in a circuit as more bulbs are added in parallel
Adding bulbs in parallel decreases the total resistance
V=IR
I = V / R
as resistance decreases, current increases for the same voltage
The IV graph below shows a line for fixed resistor. How would the line change for a resistor with half the resistance?
It would be steeper
It would have double the gradient
It would have double the current for the same volts
What is the effect of current in a resistive wire?
Moving electrons in the wire collide with the metal ions
The transfer energy electrically to the wire
The wire heats up -gains a thermal store
When hot enough the wire may glow - radiate energy
How will the current change if the resistance of a circuit is decreased for the same voltage?
current will increase
How does a fuse work?
- If the current exceed the fuse rating (sure in current)
- the fuse wire heats up and melts
- This breaks the circuit and isolate the appliance
- protecting it from overheating/fire
To investigate how the currect varies with voltage in a filament bulb, fixed resistor and diode you should use the cirucit below.
Why does the circuit need a variable resistor?
To vary the voltage across the component
Independent variable is voltage
Dependent variable is current
The plastic around wires keep us safe. Explain
Plastic is an insulator.
No current can flow through an insulator
no risk of electric shock
What is resistance?
- The tendency of a material to resist the flow of an electrical current.
- A measure of how much voltage is needed per amp of current.
How does the resistance vary with light intensity on a LDR?
As light intensity increases, resistance decreases
Below is an IV graph for a…..
diode
How is voltage related to energy and charge?
V=E/Q
Voltage = Energy / Coulomb
Voltage lost across a component is a measure of the energy lost across the component per coulomb
What is power measure in?
Watts (W)
How does an Earth wire and a fuse work together to protect the user of an appliance
- The Earth wire is connected to the metal casing of the appliance
- if the live wire works loose (fault) and touches the metal casing
- there is a surge in current through to the Earth wire
- this melts the fuse wire
- isolating the appliance
- preventing an electric shock
