P3.2 Flashcards
What is the link between potential difference, energy and charge?
Potential difference (V)
Energy transferred (J) = ———————————
Charge (C)
What is potential difference measured in?
Volts
How do you measure current in a series circuit?
With an ammeter
How do you measure potential difference in series circuits?
With a voltmeter
What happens when two voltmeters are in series?
They add up to give the total potential difference
What happens when 2 voltmeters are parallel?
They are both equal to the total potential difference
What is the formula for potential difference?
Potential difference = resistant x current
Why do some components have resistance?
They have ions in a fixed lattice and when the flow of electrons from the wire collides with the ions, resistance and what is formed
What is a variable resistor?
A circuit component that you can use to change the amount of wire or other resisting material
Why is a graph of resistance to potential difference linear?
As you increase potential difference, it’s resistance does not change
What do you use in a circuit if you need the resistance to be constant?
A resistance wire or a resistor
What is Ohm’s law?
The current is proportional to the potential difference if the temperature does not change
What is a diode?
A component that only allows a current to flow one way
What does LED stand for?
Light-Emitting Diode
How do connect an LED to a battery?
The long led of an LED should be connected to the positive terminal
What happens to the current and potential difference in a diode?
As you apply potential difference in the forward direction, very little current flows then it suddenly increases.
What happens when you reverse the potential difference in a diode?
There is no current
When would you use a diode?
When you want the current to flow in only 1 direction
What is a thermistor?
An object in which its resistance depends on temperature
What is a thermistor made of?
A semiconducting material such as silicon
What does a line of constant gradient in a current by PD graph mean?
The component is linea
What is the gradient of a current by PD graph?
Opposite of resistance
What does a steep gradient mean in a current by PD graph?
Small resistance
What does a small gradient mean in a current by PD graph?
Large resistance
What does a line of changing gradient mean in a current by PD graph?
The component is non-linear element
What is the resistance of a diode in the reverse direction?
Extremely high (infinitely high)
How does the resistance of a thermistor change with temperature?
As you increase temperature, resistance decreases
Why does an increase of temperature mean a decrease of resistance in thermistors?
As you heat it, more electrons gain enough energy to escape from the atoms in the semiconductor meaning more electrons become available for conduction
What does a thermistor look like in a circuit diagram?
A rectangle with a line thorough it which bends outside the rectangle
What does an LDR look like in a circuit diagram?
A rectangle surrounded by a circle with 2 arrows pointing at it
What does LDR stand for?
Light-dependent resistor
How does a light-dependent resistor work?
Its resistance changes with light intensity - as you increase light intensity, resistance decreases
Why does an increase of light intensity cause less resistance in an LDR?
Light causes more electrons to be released into the circuit, increasing the current
How are current and resistance related?
As you increase current, resistance decreases
What does a resistance graph for a thermistor and LDR look like?
Starts high with a curved decrease
What would happen if you add another lamp in series?
Current decreases
Net resistance increases
What happens if you add another lamp in parallel?
Total current increases
Net resistance decreases
How do you work out net resistance?
Potential difference (V)
———————————
Total current (A) - current at end of circuit
What is a milliamp?
1/1000 A
How do you calculate potential difference in a sensing circuit?
- Calculate net resistance (NR)
- Calculate the current (PD of battery over NR)
- Calculate PD of what you are looking for (I x R)
What is a kilo ohm?
1000 ohms
What is power?
The energy transferred per second
How is energy transferred related to potential difference?
Potential difference = energy transferred / charge
What is the formula for current (in terms of charge)?
Charge
————
Time
What are the equations for power?
Potential difference x current
Current^2 x resistance
What is the formula for energy transferred in Joules per Kilowatt Hour (for home appliances)?
Power (W) x Time (s)
What are the units for power?
Warrs
