AC and DC Flashcards
Current definition
Rate of flow of charge
What is current measured in
Amps
Charge measured in
Coulombs
What can result in a high current
Lots of electrons moving slowly
What is direct current
If the current only flows in one direction
What can supply DC electricity
Batteries and cells
What can current do and not do
Decrease or increase but not change direction
What is alternating current
If the current constantly changes direction and goes negative
What can supply AC electricity
Mains electricity
What is energy transferred at in a circuit
The speed of light
What is voltage
Energy per unit charge
What is potential difference
Refers to the energy converted from electrical energy per unit charge
How can we measure current in series
Using ammeter
How can we measure voltage in series
Voltmeter
What does a series circuit contain
All components in a single loop
What is a parallel circuit
A circuit containing more that one loop or branch, and may have junctions
In a series circuit the current is…
The same everywhere
In a parallel circuit, the current…
Splits at a junction. The current next to the cell is highest
Why is the current next to the cell in a parallel circuit the highest
All electrons must flow from that wire to the rest of the circuit
How can the current in a circuit be increased
- Increasing voltage supplied
- Decreasing resistance of a circuit
- Connecting the circuit in parallel (this decreases the resistance)
In a parallel circuit the voltage…
Is the same for each branch. The voltage across each branch is equal to the voltage across the battery
In series the voltage…
Along a branch, is shared between the components.
What determines the voltage across a component
The resistance of the components
What causes resistance
Electrons colliding with positive ions that form the structure of the metal wire
What happens to energy in a resistor
Chemical energy is transferred into thermal
What is resistance measured in
Ohms
What does a variable resistor do
Change the resistance in a circuit
How does a variable resistor change resistance
Increasing or decreasing the length of wire the electricity has to flow through
How does a longer length reduce current
The longer the length, the more electrons collide with ions
What does ohms law state
Current through a resistor at a constant temperature is directly proportional to the voltage across for a constant resistance
Voltage = Current X Resistance
What is an LDR
Light dependent resistor
What does an LDR do
Change resistance with light intensity
What do fixed resistors have
A constant resistance
What happens with filament bulbs
They do not obey ohm’s law
What happens with resistance for an LDR
The higher the light intensity the lower the resistance
Where can LDRs be found
Street lamps
What does a thermistor do
Change resistance with temperature
What happens with resistance in thermistors
The higher the temperature the lower the resistance
Where can thermistors be found
Kettles
