Electricity and Circuits Flashcards
What is an electric current?
The flow of electrical charge around a circuit
Which way do electrons flow in a circuit?
From - to +
Which way does conventional current flow in a circuit?
From + to -
In series circuit what does potential difference around the circuit have to add up to?
The cell voltage
What does the current in the different branches of a parallel circuit have to add up to?
The current leaving the cell
How is the current split in a series circuit?
It’s the same all around
In a parallel circuit how is the voltage split?
It’s the same all around
How do you calculate charge?
Charge (C) = current (A) x time (s)
What do you measure current with?
An ammeter
What do you measure potential difference with?
A voltmeter
How do you calculate the amount of energy transferred?
Energy transferred (J) = charge moved (C) x potential difference (V)
What is Ohm’s law?
Potential difference = current x resistance
How can the resistance of a circuit be changed?
Using fixed or variable resistors
What happens to the current as the resistance increases?
The current decreases, as the resistance decreases, the current increases
If there are two resistors in a series circuit, one with of a resistance of 2Ω and the other with a resistance of 4Ω what is the total resistance of the circuit?
6Ω
What does varying the value of a variable resistor allow you to do?
Record the current for different potential differences
What happens to the resistance when the light intensity increases (when using a light-dependent resistor)?
The resistance decreases
When using a thermistor what happens to the resistance as the temperature increases?
The resistance decreases
How can unwanted thermal energy transfers be prevented?
By using low resistance wires
When is electrical energy dissipated?
When an electrical current does work against an electrical resistance
When is the transfer of electrical energy to thermal energy useful?
- In kettles
- Irons
- Toasters
What are the disadvantages of the heating effect?
If too much current flows through the circuit then the appliance could catch fire or the user could be burned, also in many appliances the heating effect causes energy to be wasted
Why would too much current be flowing through an appliance’s circuit?
Too many appliances being used at once
Why is energy dissipated into thermal energy?
When potential difference is applied across the ends of a metal, electrons flow through the metal lattice. Electrons and metal ions collide which leads to the kinetic energy of the electrons being dissipated as thermal energy
In direct current how does the potential difference change throughout?
It doesn’t change, it’s constant
In batteries what type of current is supplied?
D.c
What is alternating current?
Current that changes direction frequently, the potential difference is constantly changing
What type of current is supplied by mains electricity?
A.c
What do earth wires and fuses do?
- If the live wire comes loose, it might touch a metal part of the device’s casing, this causes a large current to heat and this melts the wire in the fuse causing the circuit to break
- The earth wire is connected to metal casing so when a large current flows through the live wire it flows out the earth wire
- The circuit is no longer complete so there’s no chance of an electric shock or fire
What does the live wire do?
Carries the supply of current to the appliance, it has a potential difference of 230V
What does the neutral wire do?
It completes the circuit with the appliance, it has a voltage of 0V
What are the wires in a plug made from?
Copper but they’re covered in colour-coded insulating plastic
