electricity Flashcards
What is the relationship between resistance and current?
Inversely proportional- the greater the resistance, the smaller the current
What is current?
The rate of flow of charged particles measured in amperes
What is the equation for current?
Current=charge/time
What is charge?
a property of a body which experiences a force in an electric field, measured in coulombs
What is potential difference?
a measure of energy, per unit of charge, transferred between two points in a circuit, measured in volts
What is the equation for charge?
Charge = current x time
What is the equation for potential difference?
potential difference = current x resistance
What is resistance?
opposition to the flow of current, measured in Ohms
Describe the required practical investigating factors affecting resistance
- attach a crocodile clip to the wire level with 0 cm on the ruler
- Attach the second clip 10cm away
- close the switch then record the current and p.d using an ammeter and voltmeter
- open the switch and then repeat with the clip 10cm further along the wire
- calculate the resistance by dividing the p.d by the current
- plot on a graph
What is the equation for resistance?
resistance=potential difference/current
What does the IV graph for a resistor look like and what does it mean?
A resistor will have a straight line going through the origin showing that current and potential difference are directly proportional
What does the IV graph for a filament lamp/bulb look like and what does it mean?
straight line through the origin and curves once it reaches the limit of proportionality. As the current increases, the temperature of the filament increases, thus increasing the resistance, meaning less current can flow through
What does the IV graph for a diode look like and what does it mean?
a steep curve that turns into a straight line, only on one side of the graph represents current only flowing in one direction
What is an LDR?
Light dependent resistors decrease resistance in bright light and increase resistance in darkness
What is a thermistor?
A temperature dependent resistor- resistance decreases in hot conditions and increases in cold conditions
Describe the IV required practical
- set up a circuit with a variable resistor, a component and an ammeter and voltmeter
- take several readings of the ammeter and voltmeter, changing the variable resistor each time
- swap the wires to reverse the direction of current and repeat the readings
- plot the readings on a graph
In a series circuit, how are resistance, current and potential difference distributed?
Potential difference is shared, current remains the same and resistance adds up
In a parallel circuit, how are resistance, current and potential difference distributed?
Potential difference is the same, current is shared and resistance decreases by adding another resistor in parallel
What happens to resistors in parallel ciruits?
If you have 2 resistors in parallel, their total resistance is smaller than the resistance of the smallest resistor as they have the same p.d acting against them but by adding another loop, current increases, thus decreasing resistance
What will happen when you add identical resistors in series and how will that look like on a graph?
resistance increases, represented by a straight line through the origin
What will happen when you add identical resistors in parallel and how will that look like on a graph?
Resistance will decrease, represented by a downwards curve that looks like a reciprocal curve
Are mains and battery supply alternating or direct current?
Mains is alternating and battery is direct current
What us the frequency and voltage of UK mains supply?
50 Hz and 230V
What is the difference between alternating and direct current?
Alternating current is where current flows in both directions and positive and negative ends alternate whereas direct current always flows in the same direction
