Mains Electricity and Current and Voltage in circuits Flashcards
Why are the bulbs dimmer in the second circuit?
Voltage is shared between bulbs in series
Less voltage across each bulb therefore bulb is dimmer.
Adding second bulb in series, doubles the resistance of the circuit, halving the current as well - bulbs are dimmer for this reason as well.
Define voltage
Energy per unit charge either supplied by a cell, or transferred to a component.
What type of current is shown in the image?
Alternating current
Current that constantly changes direction
i.e. 50 Hz or 50 times a second
What is voltage measured in?
Volts or V
What is the voltage across a cell or power supply a measure of?
The energy transferred from chemical store electrically to the wires per coulomb
What component symbol is shown below?
bulb
What component symbol is shown below?
ammeter
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!)
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
The IV graph below shows a line for fixed resistor. How would the line change for a resistor with half the resistance?
It would be steeper
It would have double the gradient
It would have double the current for the same volts
What is the effect of current in a resistive wire?
Moving electrons in the wire collide with the metal ions
The transfer energy electrically to the wire
The wire heats up -gains a thermal store
When hot enough the wire may glow - radiate energy
How will the current change if the resistance of a circuit is decreased for the same voltage?
current will increase
To investigate how the currect varies with voltage in a filament bulb, fixed resistor and diode you should use the cirucit below.
Why does the circuit need a variable resistor?
To vary the voltage across the component
Independent variable is voltage
Dependent variable is current
The plastic around wires keep us safe. Explain
Plastic is an insulator.
No current can flow through an insulator
no risk of electric shock
What is resistance?
- The tendency of a material to resist the flow of an electrical current.
- A measure of how much voltage is needed per amp of current.
Below is an IV graph for a…..
diode
What is power measure in?
Watts (W)
What is a watt?
1 W = 1 J/s
I Watt = 1 joule per second
What is a volt?
1 V = 1 J/C
1 volt = 1 joule per coulomb
How does voltage related to current and resistance?
V=IR
What is true about the current in a series circuit?
Current is the same everywhere in a series circuit
What type of circuit is this? Series or parallel?
Series circuit
Only one path or branch in the circuit
How does voltage across bulbs 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
What is the unit for current?
ampere / amps or A
What component symbol is shown below?
buzzer
What component symbol is shown below?
voltmeter
What is the unit for energy?
joules (J)
How is power related to current and voltage?
P=IV
What component symbol is shown below?
Light emitting diode
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)
What is the difference between d.c. and a.c. current/voltage
Direct current - current flows in one direction only (i.e. cell)
Alternating current - current continuously changes direction (i.e. mains supply)
Each cell provides 3 V. In which circuit (series or parallel are the bulbs brighter?
Bulbs in parallel are brighter = both have 3V across them (brighter)
Bulbs in series have 1.5 v across each (dimmer)
Series- voltage is shared - VCell = V1 + V2
Parallel - each bulb gets the full voltage of the cell - Vcell = V1 = V2
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
Describe what it means when 1 A is passing through a circuit
1 A = 1 Coulomb per second
The IV graph below is for an ohmic conductor…
Give an example of an ohmic conductor.
- fixed resistor
- wire (if at constant temperature)
Below is the IV graph for a….
filament bulb
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 component symbol is shown below?
diode
What component symbol is shown below?
variable resistor
What component symbols are shown below?
battery/two cells
&
solar cell
