P2.3 Currents In electrical circuits Flashcards
How do insulating materials become electrically charged?
- Charge builds up when two insulators rub together - Electrons leave one surface, leaving it positive. - The other surface gets an equal negative charge - The two oppositely charged surfaces are then attracted together
What substance do electrons move easily through?
Metals
What substance do ions move easily through?
Solution
Define ‘current’
A flow of charge
What is the relationship between the size of the current and the rate of the flow of charge?
They are the same
Define ‘potential difference’
Work done per coulomb of charge as it passes between two points
Why does the resistance increase as the current goes up in a resistor?
- Electrical energy is transferred to heat energy so the resistor gets hot - Causing ions in the conductor to vibrate more - Electrons carrying charge find it hard to move through them so the current can’t move and the resistance increases
Why do filament graphs potential difference-current graphs level off?
- More current means an increase in temperature - Meaning an increases in resistance - Meaning the current decreases again
What is the relationship between current and P.D in a resistor?
Current through a resistor is directly proportional to potential difference
Why does current only flow in one direction in a diode?
The diode has a very high resistance in the opposite direction
What is the purpose of a diode in a circuit?
- It is used to regulate the potential difference in circuits, by making sure the current can only flow in one direction - It is useful in various electrical circuits
How does a thermistor act in a circuit?
- To act as a temperature dependent resistor - Hot conditions = resistance drops, current increases - Cold conditions = resistance increases, current decreases
Name 3 uses of thermistors and why.
- Car engine temperature sensors - Electronic thermostats - Fire alarms By increasing the current at high temperatures, the temperature detector can signal that the temperature is too high.
How does a LDR act in a circuit?
- It acts as a resistor dependent on light - Bright light = resistance falls - Darkness = resistance increases
Name 3 uses of an LDR.
- Automatic night lights - Outdoor lighting - Burglar detectors
How does an LED act in a circuit?
- It emits light when the current flows in a forward direction through it - They indicate the presence of a current in a circuit
Why are LEDs being used more as lighting?
They use a much smaller current than other forms of lighting.
Name 3 uses of LEDs.
- Remotes - Traffic lights - Digital clocks
What does current do in series?
It stays the same for all the components
What does current do in parallel circuits?
It is split between the devices at a junction
What does p.d do in series?
It is shared between the components in the circuit
What does p.d do in parallel circuits?
It stays the same for all the components
How are ammeters always connected to a circuit?
In series
How are voltmeters always connected to a circuit?
In parallel with a component
