Chapter 9 - Energy, Power and Resistance Flashcards
What is Potential Difference?
What happens to the Potential Difference when charge carriers go through a resistance?
What is the Equation for Potential Difference?
Work Done per unit of charge by the charge carriers doing work from an electrical to light/thermal energy store. Also a measure of difference in potential (energy) between 2 points.
Charge Carriers loose it to resistance
V = IR, V = W/Q
What is the Volt?
What happens when particles gain Volts?
1 Volt is the potential difference across a component when 1J of energy is transferred per unit of charge through a component
The particles accelerate and the work done is the same as the Kinetic Energy the electron gains
What is EMF?
Equation for EMF?
Electromotive force which is the work done per unit of charge on the charge carriers doing work from chemical to electrical energy store. Supplied in Cells/Batteries. Its energy the charge carriers gain
E = W/Q
How does the Electron Gun work?
EMF is produced to energize electrons in a filament. PD is then used to eject/accelerate them towards an anode
What is eV?
How is 1eV represented as Joules?
What is the Equation for eV?
Electron Volt, the amount of work done per unit of charge on a single electron equivalent to the Kinetic Energy on it (as it moves). KE represented as eV is also the energy an electron gains when it travels through a potential of xV.
1eV = 1.6*10^-19J of Kinetic Energy
eV = V x (1.6*10^-19)
What is Resistance?
What is the Equation for Resistance?
A hindrance to Current, the amount of energy required per Ampere to get through
R = V/I
What is the Equation for Resistance in terms of Resistivity?
What is resistance proportional to?
What is Resistance inversely proportional to?
R = pL/A
R = Resistance
p = resistivity
A = Cross Section Area
p and L (as the long the wire, the more lattice the charge collides with)
A as increasing Cross Section Area makes current easier to pass, decreasing resistance
What is the relation between resistance and Semiconductors (Specifically temperature relation)?
As temperature increases, more charge carriers are released due to NCT material which reduces the resistance
What is Resistivity?
Unit for Resistivity?
What is the symbol for Resistivity?
What is the Equation for Resistivity?
Fixed Physical Property of Materials which determines how much Charge it resists.
Ohmic Meters
p (rho)
p = RA/L
When would Resistivity Differ?
When the temperature changes, as the lattice vibrates more which means more frequent collisions
What happens to the resistance if the length doubles?
What happens to the cross section area if radius doubles?
The resistance doubles due to it being in proportion
Cross section doubles as pir^2 becomes pi(2r)^2 becoming pi4r
How can we determine Resistivity?
Use vernier calipers to measure the cross section area of you wire, by taking averages. Create a circuit made of your wire, Ammeter and Voltmeter to calculate units and work out the Resistance. Then use the equation to work out p (resistivity)
What is a Superconductor?
Occurs when a material is cooled so much that resistance = 0, so no energy is lost by the charge to get through the wire
What is Ohms Law?
What happens if temperature of a wire increases?
How does the resistance increase?
PD in a wire is proportional to current if temperature remains constant
If temperature increases, resistance would increase, but PD stays constant and current decreases
Increase in temperature makes the lattice vibrate creating internal resistance which collide with charge carriers more frequently
What is an IV Characteristic
How do you setup an IV characteristic?
A graph showing the relation of current and PD in a component with the gradient showing the resistance
Circuit with Voltmeter, Ammeter, Cell/Battery, desired component set up. Connect a type of resistor to vary the current/pd to get many values and plot it into a graph
How can we alter the current or PD using a component(s)?
Using a variable resistor or potentiometer
Describe what the IV of a Fixed Resistor looks like?
Describe what the IV of a Filament looks like?
Ohmic as the gradient remains constant as resistance doesn’t differ despite environmental changes
Non-Ohmic, at high resistance where the current is small is proportional, but as it increases, internal resistance in created which reduces the current per pd near the ends of the graph
Describe what the IV of a Diode looks like?
Non-Ohmic as its made of semi-conductors. It only has 1 value as there’s infinite resistance in the other side. The other side needs a threshold of PD to get through. Resistance decreases as PD increase due to releasing more charge carriers, making the current increase rapidly
What is an NCT Thermistor?
Semi-conductors made of NCT which increases density of charge carriers, decreasing resistance as temperature increases. This is good to monitor temperature control
Describe what the IV of a NCT Thermistor looks like?
Non-Ohmic due to NCT, current increases at a faster rate than the PD which is why current goes upwards rapidly at the end.
Describe what the IV of a LDR looks like?
Non-Ohmic and made of Semi-Conductors. Its resistance decreases when light intensity increases as number density of charge carriers increase
How is energy usually transferred?
From a power source, to a component, to forms of energy
Define Electrical Power?
Symbol and Units for Power?
Equations for Power
Rate of energy transfer by each component per unit of time
W, Js^-1
P = W/t, VQ/t, VI, I^2R, V^2/R
What is Work Done?
Equations for Work Done?
Total energy transferred by a component by multiplying the duration it was on by the power of the component
W = VIt, Pt
Equation for cost in terms of Power?
Cost = kWh*Cost per kWh
What is resistance proportional/inversely proportional to and how?
Directly proportional to the length of a wire as there will be more collisions between the charge carriers and lattice
Inversely Proportional to the Cross Section Area as charge
Directly Proportional to temperature (conductors) (Semi Conductors) resistance is inversely proportional
What is a Cell/Battery?
Does work/provides energy on the charge carriers, supplying PD
What is a Switch?
What is a Capacitor?
What is a Power Supply?
Controls whether current could flow along a piece of wire or not
Stores/releases potential difference
Supplies PD to an electric load
What is a Filament?
What is an Ammeter?
What is a Volmeter?
A component that lights up where current passes through it
In series, it measures the current in the circuit
In parallel, it measures the difference in potential/energy between to points before/after a component
What are resistors?
What is a Variable Resistor?
A component which resists current, which needs energy to get through
A resistor that can vary its resistance
What is a thermistor?
What is a LDR?
A resistor which increases resistance according to temperature
A resistor which increases resistance according to the measure of light intensity
What is a Diode?
What is a LED?
A component that allows current to flow in 1 direction, the forward bias, rather than the opposite way, reverse bias
A diode that lights up, usually used in street lamps
