Section 5 - Electricity And Circuits (Unfinished) Flashcards
Define the term current
It is the rate of flow of electric charge (electrons) through a circuit
What is the unit for current?
Ampere, A
What is the potential difference?
Is the energy per unit of charge that is transferred by the component
What is potential difference measured in?
Volts, V
What is resistance?
The ratio of voltage over current - it is how much the current is limited
What is the unit for resistance?
Ohms, Ω
How does potential difference generally affect the current?
The higher the potential difference, the higher the current
How does resistance affect the current?
The greater the resistance, the lower the current
What is the equation for charge?
Charge = current x time
How do you calculate energy transferred?
Energy transferred = charge moved x potential difference
How much does one volt equal in a joule our coulomb?
One volt = 1 joule per coulomb
How do you calculate potential difference?
Potential difference = current x resistance
What factor usually affects resistance?
Temperature
Why does the temperature increase when an electrical charge flows through a component?
Because work needs to be done against resistance, causing friction in the wires
What does dissipated mean?
Energy is lost to the surroundings
Why does the temperature of a resistor increase when a current flows through it?
The electrons collide with the ions in the lattice that make up the resistor, and this gives the ions more energy which causes them to vibrate and heat up
The more the ions vibrate, the harder it is for the electrons to get through the resistor, because there are more collisions
This means that the for a given potential difference, the current decreases when a resistor heats up
What affect does temperature have on a thermistor?
The resistance of the thermistor decreases as the temperature increases
What is an LDR?
A light dependent resistor
In bright light, the resistance falls
In dim light, the resistance increases
What are some common uses of LDR’s?
- Automatic night lights
- Outdoor lighting
- Burgular detectors
What is a thermistor?
A temperature dependent resistor
In hot conditions, the resistance drops
In cold conditions, the resistance increases
What are some common uses of thermistors?
Electronic thermometers
What is a series circuit?
In a series circuit, the different components are connected in a line, end to end
If you remove one component, then the whole circuit no longer functions and is broken
What is the current in a series circuit?
The current in a series circuit is the same, no matter what point you place an ammeter in the circuit
What happens to the total resistance in a series circuit when you add resistors?
The total resistance increases
What is a parallel circuit?
In a parallel circuit, each component is separately connected to the supply
If you remove one component, it will hardly affect the others, and the circuit will still work
Which is more commonly used - series or parallel circuits?
Parallel circuits - for example in household electrics - you don’t have one switch for the entire house. you have different switches which turn off different lights in different areas of the house, which is why parallel circuits are used as they are more convenient and can be used in a wider range of applications
Is the current the same across the whole circuit in a parallel circuit?
No - the energy in the circuit stays the same, but the energy is split at the different junctions. The energy going into these junctions will be added up to show that the energy in the circuit still never changes - it just gets split up for the different components
What happens to the total resistance in a parallel circuit if you add resistors?
The total resistance decreases
