Unit 2 Electricity Flashcards
(36 cards)
What is a conductor and how does it conduct electricity?
A material which allows electric current to pass through it.
In a conductor some electrons can move freely from atom to atom. These electrons are called free or delocalised electrons.
Metals and graphite are good conductors as they contain a large number of delocalised electrons
What is an insulator and why doesn’t it conduct electricity?
A material which does not allow electric current to pass through it.
In an insulator all the electrons are tightly bound to their atoms.
What is electric current?
An electric current is a flow of electric charge or charge carriers. In electrical circuits, these charge carriers are electrons.
What is conventional current?
The flow of current from the positive to negative terminal of the power source.
What is electron flow?
Electrons flow in the circuit from the negative to positive terminal of the power source.
What is the unit of charge and equation for charge?
Unit: Coulomb
1 coulomb of charge contains 6.75x10 18 electrons
Q (C) = I (A) x t (s)
I (A) = Q (C)/ t (s)
t (s)= Q (C)/ I (A)
What is another name for voltage?
Potential difference (p.d.)
Why do electrons flow from the negative to positive terminal?
Because they have a negative charge and are attracted to the positive terminal.
What is voltage measured with and how is thispiece of equipment connected to the battery?
Voltage is measured with a voltmeter which is connected in parallel with an electrical device
The positive terminal of the battery/power supply is connected to the positive/ red terminal of the voltmeter.
How do current and voltage behave in series and parallel circuits?
Series-
Current is the same everywhere
Voltage splits between components
Parallel-
Current splits between branches
Voltage is the same across each branch
What is resistance?
Resistance is the opposition to the flow of current in a circuit
It is defined as the ratio of voltage to current (i.e. R= V/I)
State Ohm’s law
The current through a conductor, which obeys Ohm’s law, is directly proportional to the voltage across it provided the temperature remains constant.
What is the equation for voltage?
V (V) = I (A) x R (ohms)
I (A) = V (V) / R (ohms)
R (ohms) = V (V)/ I (A)
What is the conclusion to the metal wire investigation (current and voltage at a higher temperature)?
- We can use the results to prove that voltage and current are directly proportional.
- The graph drawn with voltage on the y-axis and current on the x-axis produced a straight line which passes through (0,0)
This means that current and voltage are directly proportional
What value does the gradient of the voltage (y-axis) and current (x-axis) give?
Resistance (ohms)
What is the conclusion of the filament bulb experiment?
From the table of results, we can see that as current increases, resistance increases
R = V / I, the gradient of the graph represents the resistance of the filament.
As the gradient increases the resistance increases
As the current through the filament bulb increases the temperature of the bulb also increases. This means that as the temperature of the bulb increases so too does the resistance. The increased temperature of the light bulb causes heat energy to be transferred to the atoms (or ions) of the filament. The ions gain kinetic energy and vibrate more about their fixed positions.
These increased vibrations make it more difficult for the electrons to travel through the filament.
There are a greater number of collisions between the travelling free electrons and the vibrating ions of the filament wire.
The filament bulb does not obey Ohms Law, it is known as a non-ohmic conductor.
What is the general rule for resistors in parallel?
1/Rt = 1/R1 + 1/R2 + 1/R3 …
What happens to the electrons when potential difference is applied to the circuit?
The electrons will drift towards the positive terminal of the battery.
What is the conclusion to the length of wire investigation?
The resistance of the wire is directly proportional to its length - straight line that passes through the origin (0,0).
What piece of equipment is used to measure resistance directly?
Ohmmeter or Multimeter
What is the relationship between resistance and CSA?
Resistance decreases as CSA increases.
Resistance is directly proportional to 1/CSA (inverse of CSA) - meaning that RESISTANCE and CSA are INVERSELY PROPORTIONAL.
What are the equations linking constants to length and CSA?
R/L = constant
R x CSA = constant
Why does a wire heat up when electric current flows through it (heating effect of electricity)?
A metallic conductor has a large number of free electrons in it. When a potential difference is applied across the ends of a metallic wire, the free electrons begin to drift from the low potential to high potential region. These free electrons collide with the positive ions (the atoms have lost their electrons). In these collisions, the energy of the electrons is transferred to the positive ions and they begin to vibrate more violently. As a result, heat is produced. The greater number of electrons flowing per second, the greater will be the rate of collisions and hence more heat is produced.
What is the equation linking energy, power and time?
P (W) = E (J) / t (s)
E (J) = P (W) x t (s)
t (s) = E (J) / P (W)
