1. In the animation you can see:
Current The battery or source is represented by an escalator which raises
charges to a higher level of energy
Current, or electric current, is the rate of flow of electric charge As the charges move the resistor, represented by the paddle wheel,
through a medium. This charge is typically carried by moving electrons they do work on the resistor and as a result, they lose their
in a conductor such as a wire. It can also be carried by ions in an energy
electrolyte, or by both ions and electrons in plasma. By the time each charge makes it back to the battery, it has lost all
Simple terms: Current is what flows on the wire like water flowing energy given by the battery
through a hose. As the charges move through the wire, they lose no energy
Current flows from negative to positive on the surface of a conductor. The potential drop (negative potential difference) across the
It is measured in amperes or amps. resistor is the same as the potential rise (positive potential
difference) across the battery. This demonstrates that a charge
can only do as much as was done on it by the battery.
Circuits The charges are positive so this is a representation of Conventional
Video: http://www.youtube.com/watch?v=9iQhL3VTDb8 Current (the apparent flow of positive charges)
There are several kinds of circuits; however, we will only discuss the The charges are only flowing in one direction so this would be
simple circuit. considered direct current
Simple Circuit
A simple circuit is fund everywhere in the world, in homes, offices and
other places.
The simple circuit requires three things for it to work: Voltage
1. A source of electrical potential difference or voltage
Video: http://www.youtube.com/watch?v=Lklai_KXGxg
2. A conductive path
3. An electrical resistor Also called:
Despite the materials being simple, it is quite useful and common. They Potential difference
exist in flashlights, ceiling lights, doorbells, and many kitchen Potential drop
appliances. Below is an animation of what goes on in a simple circuit Electrical potential difference
where the electrical energy is shown as gravitational potential energy Electrical potential energy
(GPE). It is the difference in electrical potential between two points, or in the
difference in electrical potential energy per unit charge between two
points.

2. As the monkey does work on the positive charge, he increases the 3. Resistors – objects that are designed to have a specific resistance
energy of that charge. The closer he brings it, the more electrical so that they can dissipate electrical energy or modify how a
potential it has. When he releases the charge, work gets done on the circuit behaves
charge which changes its energy from electrical potential energy to Objects such as wires that are designed to have low resistance so that
kinetic energy. they transfer currents with the least loss of electrical energy are called
Every time he brings the charge back, he does work on the charge. If he conductors. Objects that are designed to have a specific resistance so
brought the charge closer to the other object, it would have more that they can dissipate electrical energy or otherwise modify how a
electrical potential energy. If he brought 2 or 3 charges instead of one, circuit behaves are called resistors. Conductors are made of highly
then he would have had to do more work so he would have created conductive materials such as metals, in particular copper and
more electrical potential energy. Electrical potential energy could be aluminum. Resistors, on the other hand, are made of a wide variety of
measured in joules just like any form of energy. materials depending on factors such as the desired resistance, amount
Since the electrical potential energy can change depending on the of energy that it needs to dissipate, precision and cost.
amount of charge you are moving, it is helpful to describe the electrical Factors Affecting Resistance
potential energy per unit of charge. This is known as electrical 1. The nature of the material – some materials are better conductors
potential. than others, causing less resistance. The more tightly an atom
Electrical potential – at a point within a definite space is equal to the holds on to its outermost electrons the harder it will be to make a
electrical energy (measured in joules) at that location divided by the current flow. The electronic configuration of an atom determines
charge there (measured in coulombs) how willing the atom will be to allow an electron to leave and
wander through the lattice. If a shell is almost full, the atom is
reluctant to let its electrons wander and the material it is in is in
Resistance an insulator. If the outermost shell (or sub-shell with transition
metals) is less than half full then the atom is willing to let those
electrons wander and the material is a conductor
2. The thickness of the conductor/wire – the larger the wire, the less
Resistance is how much an object resists the flow of electrons. It is the
resistance; the bigger the cross sectional area of the wire the
inverse of conductance. It measures how difficult it is for electrons to
greater the number of electrons that experience the ‘electric
flow through a material. It is measures in ohms.
slope’ from the potential difference. As the length of the wire
Think of current like water flowing through a hose, if there is nothing does not change each cm still gets the same number of volts
in the hose, then the water will flow freely. However, if there is a across it – the potential gradient does not change and so the
something blocking the hose such as leaves, small animals, pebbles, etc. average drift velocity of individual electrons does not change.
then it will be harder for the water to flow through. Although they do not move any faster there are more of them
Conductors, Insulators and Resistors moving, so the total charge movement in a given time is greater
1. Conductor – a material which contains movable electrical and current flow increases. This does not give rise to a straight
charges. In metallic conductors such as copper and aluminum, line graph as cross sectional area is inversely proportional to
the movable charged particles are electrons resistance not directly proportional to it.
2. Insulator – a material that is a poor conductor of electricity. 3. The length of the conductor/wire – the longer the wire, the more
- An insulator, such as ceramic or rubber, has high resistance; if you take a wire of different lengths and give each a
resistance and poor conductance. A metal has low particular potential difference across its ends. The longer the
resistance and high conductance wire, the less volts each cm of it will get. This means that the
‘electric slope’ that makes the electrons move gets less steep as

3. the wire gets longer, and the average drift velocity of electrons
decreases. The correct term for this ‘electric slope’ is the
potential gradient. A smaller potential gradient (fewer volts per
meter) means current decreases with increased length and
resistance increases.
4. The temperature – heat affects resistance, the higher the
temperature the higher the resistance. When you cool a certain
material to a the point where it reaches its critical temperature,
its resistance would equal zero. But if you increase its
temperature, you’d give more energy to its atoms, this increasing
the number of collisions between them resulting in increasing the
resistance
Ohm’s law
Ohm’s Law describes mathematically the relationship between current,
voltage (potential difference) and resistance. The more potential
difference you have, the greater your current is going to be. The more
resistance a circuit has, the lower the current is going to be. The
I is the current through the conductor in units of amperes;
following equation describes Ohm’s Law. It holds true for any circuit as
long as temperature does not change. V is the potential difference measured across the conductor in units of
volts; and
R is the resistance of the conductor in units of ohms.
The potential difference (voltage) is proportional to the current
through it. The current is indirectly proportional to resistance.