5.1 - Current Electricity

Created by

Dan Roper

Cards (24)

What is electric current? State its units
The rate of flow of charge. It is measured in amperes (amps).
What is potential difference?
The work down moving a unit charge between 2 points in a circuit V = W / Q
What is resistance? 
How difficult it is for current to flow through an appliance. A component has a resistance of 1 ohm if 1A flows through it when a pd of 1V is applied across it.
R = V / I
What is meant by an ohmic conductor?
A conductor that obeys Ohm's Law, meaning that current is directly proportional to potential difference providing physical conditions (such as temperature) remains constant
How can you measure the current in a circuit?
By using an ammeter that is connected in series with the component
How do you measure potential difference across a component?
By using a voltmeter that is connected in parallel with the component you are measuring the pd across
What does the gradient of current-potential difference graph represent?
Rate of change of current with respect to voltage, which is not the same as 1/R
Why does the current increasing on a filament lamp cause an increase in the resistance?
As current flows through the lamp, electrical energy is converted to heat energy so the metal ions vibrate with increased amplitude. This impedes the movement of electrons through the lamp as they collide with ions (resistance has increased).
What is a diode?
A diode is an appliance that only allows current to flow in one direction
What is a Light Dependent Resistor (LDR)?
A semiconductor that is sensitive to light.

As the light intensity increase, the resistance decreases.
How does a thermistor work?
Similar to an LDR, but, as the temperature increases, the resistance decreases.
This means that thermistors have a negative temperature coefficient.
What is resistivity? 
The resistance of a 1m length component with a 1 m^2 cross-sectional area. It is a property of a material.
p = RA/L
Describe an experiment to determine the resistivity of a wire.
1. Measure the diameter of the wire using a micrometer and then calculate the cross sectional area
2. Set up the circuit as shown
3. Vary the wire length and record the voltage and current for each length
4. Use R=V/I to determine the resistance
5. Plot a graph of resistance against wire length
6. The gradient = resistivity / cross-sectional area
7. So resistivity = gradient * cross-sectional area
What is a superconductor?
A material that has a resistivity of 0 at or below a critical temperature.
The critical temperature is an inherent property of a material
How do you find the total resistance in a series circuit?
Add the individual resistances of each component
How does the current vary between each component of a series circuit?
The current through all of the components is the same so the current does not vary
Is the current in parallel components the same?
No, each branch of a parallel circuit can have different currents through them according to Kirchhoff's first law
What is Kirchhoff's First Law?
The total current entering a junction = the total current leaving it
What is Kirchhoff's Second Law?
For any path (loop) of a circuit, the sum of all of the potential differences must equal to total emf of the circuit.
In a series circuit, if two cells are connected together negative to negative, would their emf add up or cancel out?
They will cancel out.
What is power? 
The rate of energy transfer
What is the purpose of a potential divider?
- To provide variable potential difference
- To provide a constant specific potential difference
What is emf? 
Electromotive Force - the electrical energy transferred by a power supply per unit charge
What are two applications of superconductors?
● Power cables, which would reduce energy loss through heating to zero during transmission.

● Strong magnetic fields, which would not require a constant power source. These could be used in maglev trains, where there would be no friction between the train and rail, and in certain medical applications