topic 2 - electricity: current, potential difference and resistance Flashcards
What must a circuit include for charge to flow through it?
A source of potential difference.
What is current?
A flow of electrical charge.
What is the equation that links charge flow, current and time?
Charge flow = current x time
What is the symbol for charge?
Q
What is the symbol for current?
I
What is the symbol for time?
t
What is charge measured in?
Coulombs (C)
What is current measured in?
Amperes (amps) (A)
What is time measured in?
seconds (s)
At any point in a single closed loop, what is true of the current?
It has the same value.
What is another name for potential difference?
Voltage
What is the equation that links potential difference, current and resistance?
potential difference = current x resistance
What is the symbol for potential difference?
V
What is the symbol for resistance?
R
What is potential difference measured in?
Voltage (V)
What is resistance measured in?
Ohms (Ω)
When resisitance is increased, what happens to the current?
It decreases for a given potential difference across the component.
Is the current in an ohmic resistor directly proportional or not? (at a constant temperature)
Yes - this means that resistance remains constant as current increases.
Give examples of at least 2 components where resistance is not constant.
Lamps, diodes, thermistors and LDRs.
What is the relationship between resisitance and temperature in a filament lamp?
Resistance increases as the temperature of the filament increases.
How many directions does the current flow through a diode and why?
One direction only - the diode has a very high resistance in the opposite direction.
What is the relationship between resisitance and temperature in a thermistor?
Resistance decreases as temperature increases.
What is the relationship between resisitance and light intensity in a LDR
Resistance decreases as light intensity increases.
Give one everday itrem where a thermistor is used.
A thermostat
Give one everyday use of an LDR
switching lights on when it gets dark
What device do you use to measure current?
An ammeter
Should an ammeter be placed in series or parallel?
In series
What device do you use to measure potential difference?
A voltmeter
Should a voltmeter be placed in series or parallel?
In parallel
