10 Energy and Voltage- 4th Form 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
Define voltage
Energy per unit charge either supplied by a cell, or transferred to a component.
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?
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
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
They 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 (surge 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.
Below is an IV graph for a…..
diode
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
What are the prongs of a plug made of brass but the wires made of copper?
Brass is strong and will not bend
Copper is a good conductor of electricity and ductile (can be drawn into wires)
Below is the symbol for…
a double insulated appliance
What is the Earth wire connected to in the appliance
The metal casing
What component symbol is shown below?
voltmeter
What component symbol is shown below?
Fuse
Name the parts of a plug
- Cable grip
2 Neutral wire
- Earth wire
- Live wire
- Fuse
What is the difference between d.c. and a.c. current/voltage
Direct current - current flows in one direction only (i.e. cell)
Alternating current - current continuously changes direction (i.e. mains supply)
The IV graph below is for an ohmic conductor…
Give an example of an ohmic conductor.
- fixed resistor
- wire (if at constant temperature)
Below is the IV graph for a….
filament bulb
What component symbol is shown below?
variable resistor
What component symbols are shown below?
battery/two cells
&
solar cell
What would happen if a plug is wired incorrectly and the live wire is attached to the Earth prong
The Earth prong is wired to the metal casing of the appliance
The metal casing of the appliance will be live with 240V wired to it.
Risk of electric shock to user
