2c Energy and Voltage in Circuits Flashcards
What is current?
The rate of flow of charge
What is current measured in?
Current is measured in amperes (amps) which have symbol A
What can you conclude about the current in a series circuit?
The current in a series circuit is always the same at all positions no matter where you measure from
What can you conclude about the current in parallel branches?
- Current splits at junctions and adds up at junctions to give the total current
- Total current into a junction = total current out
What is the equation for charge?
Charge = Currant x Time
Q = IxE
What is charge, current and time measured in?
Charge - Coulomb - C
Current - Amps - A
Time - Seconds - S
What is voltage?
Voltage is energy transferred per unit charge
What happens when there is a higher voltage of battery?
So the higher the voltage of a battery, the more energy it gives to the electrons, the higher the voltage across a bulb, the more energy it takes from electrons
What do we measure voltage by?
We measure voltage using a voltmeter, connected is parallel
The units of voltage are Volts
What conclusion can you make about the voltage is series circuits
The sum of voltage across each component adds up to the voltage in the battery
What conclusion can you make about the voltage in parallel circuits?
The voltage in the bulbs is similar/same to the voltage in the battery
What is the current and voltage in series circuits?
Current is the same at all points in a series circuit but splits at junctions in parallel circuits
What is current and voltage in parallel circuits?
Voltage is split across components in series but is the same across parallel branches
What is resistance?
- Resistance is the opposition that an electrical device has to the flow of electrical current.
- The higher the resistance the lower the current
What is the equation for resistance?
Resistance = voltage/current
What is resistance measured in?
Ohms
How is the voltage and current affected in a fixed resistor/metal wire?
- Straight line through origin: the wire or resistor obey’s Ohm’s law which states that the current is proportional to the voltage
- Graph same in both directions because reversing the voltage changes the direction of the current but not its size
- The straight line is only produced if the temperature of the resistor/wire does not change. If the wire/resistor gets hotter its resistance increases
How is voltage and current affected in a filament bulb?
- As the current across the bulb increases, its temperature rises
- The resistance of the bulb increases as the temperature increases
- So the bulb does not obey Ohm’s Law as current is not proportional to voltage
What is the equation for energy transferred?
energy transferred = charge x voltage
E=Q x V (J per coulomb=C x V)
or
voltage = energy transferred/charge
What is potential difference?
- Is a measure of energy, per unit charge, transferred between 2 points in a circuit
- Measured using a voltmeter
What is an LDR?
- An LDR is an electric component whose resistance varies with light intensity
What is a thermistor?
- A thermistor is an electric component whose resistance varies with temperature
How is resistance affected by a thermistor?
- Resistance decreases when temperature increases
How is resistance affected by an LDR?
- Resistance decreases when the light intensity increases
How is current affected by a thermistor?
The higher the temperature, the higher the current
How is current affected by an LDR?
The higher the illumination, the higher the current
Why is the current in a solid metallic conductor is a flow of negatively charged electrons?
- The current in a solid metallic conductor is a flow of negatively charged electrons (sea of delocalized electrons).
- It is conserved at a junction because this is where it splits in a parallel circuit.
- So the total amount flowing into the junction is equal to the amount flowing out.
