Chapter 9 - Energy, power and resistance Flashcards
symbol for a cell
Just 1 cell
symbol for a battery
More than 1 cells
symbol for diode
A triangle and a line.
It only lets current flow in one direction.
symbol for a variable resistor
a resistor with an arrow going up
You can adjust the amount of resistance if can offer.
symbol for a fuse
a box with the wire going through
symbol for a thermistor
a resistor with a hockey stick going through it
changes resistance based on temperature
symbol for LDR
resistor with 2 arrows going into it (the left side)
ldr- light dependant resistance
symbol for LED
A diode with 2 arrows going away from it (the right side)
led- light emitting diode
symbol for capacitor
a battery expect that the 2 lines are the same
what is 1 volt
the pd across a component when 1J of energy is transferred per unit of charge
SI units for 1V
V = W / Q V = J / C V = kg⋅m2⋅s−2 / As
Why do voltmeters have the highest resistance?
It’s so that no current can pass through them. If it did, it wouldn’t be able to measure the difference between them.
EMF
Electromotive Force
The source of current such as a cell or a power supply.
Difference between emf and pd
Potential difference is the energy dissipated as the unit charge passes through the components. The emf is the source of this current.
Equation for emf
EMF = W / Q
Energy transfer for electrons
eV= 1/2 mv^2
What is an electron gun
It is used to produce a narrow beam of electrons, which can have precisely determined kinetic energies.
Explain how an electron gun works
If the source is a filament that is heated up to release electrons, this process is called thermionic emission. The electrons on the filament gain kinetic energy, and some may actually leave the filament. Then they go through a very small slit (anode) to produce a thin beam of electrons. As they accelerate towards the anode, they gain kinetic energy.
mass of an electron
1.1 * 10 -31
What is resistance
It restricts the flow of charge carriers through it.
equation for resistance
V = IR
Ohm’s Law
For a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the pd across it.
(aka if pd is doubled, current also needs to be doubled)
how does resistance change with temperature
the current in the circuit changes because the temperature of the wire increases over time as a result of heating caused by the current. As the wire gets hotter, the resistance increases.
How do ions relate to resistance
Ions have more energy, therefore they vibrate with a greater amplitude, so the frequency of collisions increases and charge carriers do more work and transfer more energy.
What is power
It is the rate of energy transfer by each electrical component is the power.
Equation for power
P = I2 R P = V2 / R P = VQ / t
