The resistance is influenced by the resistivity constant of the object (determined by the material it is made out of). The resistance of an object is proportional to its length (L) and inversely proportional to its cross-sectional area (A). A conductor which obeys Ohm’s law has a constant resistance and is called an Ohmic conductor.Ī non-ohmic conductor portrays a graph that does not have a constant gradient (non-linear).
If we plot current versus potential difference, the slope of the resulting graph is constant.Ohm’s law states that the current flowing through a conductor is proportional to the electric potential difference across the conductor. It is given by the ratio between the electric potential difference (V) and the current induced (I). The resistance (R) of an object can be seen as a measure of opposition to electric current through the object. For a complete loop of an electrical circuit all of the electric potential rises added together must equal all of the electric potential drops added together. Kirchhoff’s loop rule is a statement of the conservation of electric potential energy per charge. The sum of all currents flowing into a junction must equal the sum of all currents flowing out. Kirchhoff’s junction rule is a statement of the conservation of charge flow per time.
Resistors can be connected in series or in parallel.Ī voltmeter is used to measure the potential difference between two points.Ī voltmeter should be connected in parallel with the components being measured.Īn ideal voltmeter has infinite resistance.Īn ammeter is used to measure the current passing through a point.Īn ammeter should be connected in series at the point of measurement. Voltage is analogical to the differences of upstreams and downstreams where water flow in the stream is the flow of electrons within the circuit.ĥ.2 – Heating effect of electric currentsĪn electric circuit is an interconnection of electrical components in a closed loop.Ī resistor is an electrical component which implements a specific resistance within an electric circuit.Ī resistor with adjustable resistance is called a variable resistor. The electric potential difference (pd) between two points is equal to the work done (energy) required per unit charge to move from one point to another. The direction of an (conventional) electric current is opposite to the direction of electron flow.ĭirect current (dc) is a uniform current flowing in one fixed direction in a circuit.ĭirect current is usually supplied by acid-based batteries or dry cells. The existence of an electric potential difference (see the last section of 5.1) across an object causes charges to flow through the object.Įlectric current (I) refers to the rate of flow of electric charge and can be given by the equation Therefore, since F = qE = kqq/r^2, we can deduce that for non-uniform electric fields, the electric field strength can be calculated byīy cancelling out q (charge) on both sides.įor uniform electric fields, the electric field strength can be calculated by Where F is the force, q1 and q2 are the charge of the two objects (usually the same when considering two electrons), and r is the radius/distance between the two charges. This is known as the “edge effect”.Įlectric field strength (E) is the force per unit charge experienced by a positive test change placed in a field. The electric field lines curve outwards near the edge of the plates. For a uniform electric field, the field lines are straight, parallel and equally spaced.
This is due to the presence of free electrons in solid conductors. FYIĬonductors are materials which allow the passage of electric charge. While charges could migrate from one body to another, the total charge remains the same.
The charge of one electron is equal to 1.6*10^-19C.Įlectric charge is always conserved. The unit of electric charge is coulomb (C). 5.1 – Electric fieldsĮlectric charge can either be positive or negative.Ĭharges with the same sign repel each other and changes with the opposite sign attract.Īn object with equal amounts of positive change and negative charge is said to be electrically neutral.