Chapter 9 - Energy, Power And Resistance Flashcards
What is the function of the cell ?
Pushes charge around the circuit
What is the function of a Ammeter ?
Measure the current in the circuit
What does the Voltmeter do ?
It measures the Voltage or pd in a circuit
What does a filament lamp do ?
A filament lamp emits light when current passes through it
What is an LDR and what does it do ?
An LDR is a Light dependent resistor
In bright light the resistance falls
In darkness the resistance is highest
What does a fuse do ?
A fuse contains a piece of wire that melts easily so if there is a very high current going through the fuse the write heats up until it breaks the circuit.
Basically the fuse breaks the circuit in order to protect the wiring
You can get fuses that melt at different currents
What does a resistor do ?
A resistor limits the electric current in a circuit
What does an LED do ?
A Light emitting diode, emits light when a electrical current passes through it
What does a switch do ?
A switch can be used to cut off the current being pushed around a circuit. It can be used to break the circuit and can be used to complete a circuit
What is a thermistor ? And what does it do ?
A thermistor is a temperature dependent resistor.
In hot conditions, the resistance falls
In cool conditions, the resistance goes up
What is a variable resistor ?
A variable resistor is one that can have its resistance varied and therefore can also vary the potential difference/current
What is voltage a measure of ?
Voltage is a measure of the electrical energy transferred per unit charge.
It can be defined as the amount of work done per unit charge
What is voltage a difference of ?
Voltage is measured as a difference in energy between 2 points. Thus a voltmeter must be connected in parallel and is used to measure the difference in pd across a device
Whats the equation for voltage ?
V = W / Q
What is one Volt defined as ?
One volt is defined as the energy transferred Per coulomb of charge as the charges move between 2 points in a circuit
Whats the resistance of the voltmeter and why ?
You don’t want any current flowing through the voltmeter so company’s make them have a very high resistance ( infinite resistance )
What does 1V =
1V = 1JC -1
What’s the electromotive force ?
EMF is the energy transferred to the charge carriers by the cell/battery
What is potential difference ?
Pd is the energy transferred by the charge carriers ( the work done by the charge carriers )
Whats the term used to describe when work is done ?
The term used to describe when work is done is energy transferred
What is resistance of a component ?
The resistance of a component is defined as the ratio between the potential difference across the component and the current flowing through it
What is the equation for resistance ?
R = V / I
Or V = IR
Whats resistance measured in ?
Ohms ( Omega symbol )
What is one Ohm equal to ?
1 ohm = 1 VA -1
What is Ohms law ?
For a metallic conductor at a constant temperature, the pd across the conductor is directly proportional to the current flowing through it
Ohms law essentially = V = IR
How do you calculate the resistance from an IV graph ?
The gradient is the resistance
Why does resistance increase with temp ?
Because when the metal gets hotter, the metal ions inside the lattice start to vibrate move and therefore make it harder for the charge carriers to flow through them.
What is Kirchhoff’s second law ?
In any circuit, the sum of the electromotive forces is equal to the sum of the pd around a closed loop
What physical quantity conserved in Kirchhoff’s first law ? And second law
Charge is conserved in the first law
Energy is conserved in the second law
What is terminal pd ?
It’s the amount of energy available to the rest of the circuit after some of the energy has been lost in the cell as heat due to the internal resistor inside the cell
What is the lost energy called that happens due to the internal resistance of the cell ?
Lost Volts
How is the terminal pd found out ?
It’s the e.m.f supplied to the cell, minus the energy lost (lost volts) in the cell as heat
What does electromotive force =
Terminal pd + lost volts
What is resistance ?
Resistance is a measure of the opposition to current flow in an electrical circuit
What does resistance depend on ?
- cross sectional area
- material
- length
- temperature
How is resistance affected by length ?
Resistance is directly proportional to length
How is resistance affected by cross sectional area ?
Resistance is directly proportional to cross sectional area
What is resistivity ?
The measure of how much a particular material opposes electron flow is called the resistivity of the material.
What is resistivity usually given in ?
resistivity is usually given the symbol p - Greek letter rho
Whats the equation for resistivity ? How do you re arrange for rho ?
Resistivity = resistance x cross-sectional area / length
Resistance = p
Cross sectional area = A
Resistance = R
Weird p = R x A / L
