Unit 5 Electricity Flashcards
Define electric current
Rate of flow of charge
What does an electric current on one amp represent?
Rate of flow of charge of one coulomb per second
Define potential difference
Work done per unit charge
What is the resistance of a component?
Measure of how much a component opposes the flow of current
How can the resistance of an electrical component be found?
Measure the current through it and the potential difference across it
State Ohm’s law
Current through a metallic conductor is directly proportional to the potential difference across it, provided the physical conditions of the conductor do not change
What is the name for a conductor that obeys Ohm’s law?
Ohmic conductor - constant resistance
Describe the I-V characteristic for an ohmic conductor
Straight line graph through the origin
Describe the I-V characteristic for a filament lamp
Curve with a decreasing gradient
As more current flows through the filament, the temperature increases. The atoms and ions in the wire vibrate more, and collide more often with the electrons flowing through it so there is more resistance.
Describe the I-V characteristic for a diode
With forward bias, graph starts at (0/0) and increases gradually
With reverse bias, graph extends along the potential with almost zero current
What is a negative temperature coefficient thermistor?
Component for which the resistance decreases when temperature increases
What is a superconductor?
Material with zero resistivity at and below a critical temperature
Why are superconductors useful?
Current in a superconductor has no heating effect so no energy is lost
State the law of conservation of charge
Charge cannot be created or destroyed, so the amount to charge in a closed systems remains the same
State Kirchoff’s first law
Total current leaving any junction in a circuit is equal to the total current entering that junction
Define the potential difference between two points in a circuit
Energy transferred per coulomb of charge that flows from one point to the other
What is a potential drop in a circuit?
Potential difference between two points in a circuit if the charge carriers lose energy
State Kirchoff’s second law
Sum of the e.m.f.s around any loop in a circuit is equal to the sum of the p.d.s around the loop
Give the potential difference rule for two or more components in series
Total potential difference across all the components is equal to the sum of the potential differences across each component
Give the equation for calculating the total resistance for two or more resistors connected in series.
R(total) = R1 + R2 + R3. + …
What can a potential divider circuit do as part of a sensor circuit?
Supply a potential difference that varies with physical conditions, such as temperature or light intensity
What is a potentiometer?
Variable potential divider that uses a single variable resistor to allow V(out) to be varied from 0V to the maximum source potential difference
Define the electromotive force of a power supply and give its unit
Electrical energy per unit charge produced by the source, in volts
What is internal resistance?
The resistance to target flow of current inside the power supply due to the collisions between the electrons in the current and the atoms in the supply
Give the equation for calculating the lost potential difference across a power supply’s internal resistance
Lost volts = I x r
What is the benefit of connecting cells in parallel?
Providing longer lasting energy supply because the total store of energy is greater
