Electricity Flashcards
If voltage not constant, what does this mean
there is internal resistance
Why voltage decrease as brightness increases
Current increase, an increase in lost volts due to internal resistance
thus terminal pd decreases
Features of finding out greatest resistance in ohmic graph
⦾ Starts from origin
⦾ Increase at same rate throughout
⦾ Must have lowest current
What is the resistance of an ideal ammeter and voltmeter?
⦾ 0 in ammeter
⦾ infinite in voltmeter
Does a heater obey Ohm’s law
No as temperature is changing so does the resistance
What happens to the voltmeter when temperature increases? (connected to other resistors in series)
Resistance decreases
its share of emf decreases
so resistors will have an increase in pd
so voltmeter increases
What to do: to obtain I/V data below 0A in superconductor diode
reversing the battery or diode
Why rms voltage is lower than 230 for appliances when connected to cable with resistance?
there p.d. in cable
so total: 230 - in cable = hence lower
Why a cable should have low resistance?
minimise power loss
prevent overheating
What happens when the sliding contact slides far apart in variable resistor (series with lamp)
resistance increases
reduces current in component
What happens when the sliding contact slides far apart in variable resistor (parallel to lamp)
resistance increases
reduce current in battery
reduces lost volts and increase terminal pd
lamp brighter
What is meant by non-ohmic conductor
not have a constant resistance
pd. across the component is not proportional to the current in the component
What happens when light intensity of LDR increases to voltmeter (parallel)
resistance of LDR decreases
reading of voltmeter increases as it has a greater proportion of voltage
How potential difference across the terminals of cell varies with current?
As current increases, voltage decreases. (straight)
what is emf
energy transferred per coulomb of charged is moved around a circuit
