3 Energy and Voltage Flashcards
What is the unit for current?
ampere / amps or A
Define current
The rate of flow of charge OR the number of coulombs passing a point in a circuit per unit time (It is not the speed of the electrons!)
Describe what it means when 1 A is passing through a circuit
1 A = 1 Coulomb per second
What is the unit for energy?
joules
How is energy related to current, voltage and time?
E = IVt
What is voltage measured in?
Volts or V
Define voltage
It is the energy per unit charge either supplied by a cell, or transferred to a component.
How does voltage related to current and resistance?
V=IR
What is a volt?
1 V = 1 J/C 1 volt = 1 joule per coulomb
What is resistance?
a measure of how much voltage is needed per amp of current. It is a measure of the is a measure of the tendency of a material to resist the flow of an electrical current.
How is power related to current and voltage?
P=IV
What is power measure in?
Watts (W)
What is a watt?
1 W = 1 J/s I Watt = 1 joule per second
How is voltage related to energy and charge?
V=E/Q
Voltage = Energy / Coulomb
Voltage lost across a component is a measure of the energy lost across the component per coulomb
What is the voltage across a cell or power supply a measure of?
The energy transferred from chemical store to electrical in the wires per coulomb
What type of circuit is this? Series or parallel?
Series circuit
Only one path or branch in the circuit
What component symbols are shown below?
battery/two cells
&
solar cell
What component symbol is shown below?
variable resistor
What component symbol is shown below?
thermistor
What component symbol is shown below?
ammeter
What component symbol is shown below?
diode
What component symbol is shown below?
buzzer
What component symbol is shown below?
motor
What component symbol is shown below?
voltmeter
What component symbol is shown below?
bulb
What component symbol is shown below?
Fuse
What component symbol is shown below?
Light emitting diode
What component symbol is shown below?
Light dependent resistor
How does voltage across bulb in a series and parallel circuit differ?
Current is conserved in all circuits
Series - current is the same everywhere in the circuit
Parallel - current splits between the branches- current into a junction equals current out of a junction
How does current differ between series and parallel circuits?
Current is conserved in all circuits
Series - current is the same everywhere in the circuit
Parallel - current splits between the branches- current into a junction equals current out of a junction
Each bulb provides 3 V. In which circuit (series or parallel are the bulbs brighter?
Series- voltage is shared - VCell = V1 + V2
Parallel - each bulb gets the full voltage of the cell - Vcell = V1 = V2
Bulbs in parallel are brighter = both have 3V across them (brighter)
Bulbs in series have 1.5 v across each (dimmer)
Bulbs in series provide a larger resistance than bulbs in parallel
With this in mind, which circuit draws a larger current from the cell?
V = IR
I = V / R
as resistance decreases, the current increases for the same voltage
The second circuit draws a larger current from the cell, bulbs are in parallel and the total resistance is smaller than the first circuit (series circuit)
Why are the bulbs dimmer in the second circuit?
Voltage is shared between bulbs in series
Less voltage across cell therefore bulb is dimmer.
Explain why the second circuit draws a lower current from the cell?
circuit with two bulbs in series - has larger resistance
V=IR
I = V/R
as resistance increases, current decreases for same voltage
What is true about the current in a series circuit?
Current is the same everywhere in a series circuit
What happens to the total resistance and current in a circuit as more bulbs are added in parallel
Adding bulbs in parallel decreases the total resistance
V=IR
I = V / R
as resistance decreases, current increases for the same voltage
How does the resistance of an LDR vary with light intensity?
As light intensity increases, resistance decreases
