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Electricity and Magnetism (Magnetism (magnetic field (image, image), the…
Electricity and Magnetism
Repulsion and Attraction
Charges
electrons have negative charge; protons have an equal positive charge; neutrns have no charge
electrical charges can be positive (+) or negative (-)
the closer the charges, the greater the force between them
creating charge
A neutral object can become negatively charged when electrons get transferred from another object (see example by clicking on the link below)
Link Title
Electric Field
surrounds an electric charge, and exerts a force on other charges in the field, attracting or repelling them. Electric fields are created by electric charges, or by time-varying magnetic fields.
diagram
Repulsion: like charges
Attraction: unlike charges
Current
current: electric current is defined as the rate at whihch electric charges flow through a conductor
current is measured in ampere (A) by using an Ameter which is place in series of a circuit
current = charge/time
current flow in circuit
in an electric circuit, the current is due to the flow of free electrons
electrons flow from the negtive terminal of the battery
measuring current in parallel circuit
current is equally distributed at all points
I = I1 + I2 + I3
Potential Difference
potenital difference: the work done in taking a unit charge from one point of the circuit to another
SI unit for potential difference is volt (v); potential difference is measured with a voltmeter (placed in parallel to circuit )
voltage: potential difference between 2 points in an electric field is defined as the work done/ the energy would be required to move 1 unit of charge from 1 point to another
voltage in parallel circuits
potential difference is the same at all points
V = V1 + V2 + V3
potential difference = work done / charge
resistance
resistance: a measure of the opposition to current flow in an electrical circuit
resistance of a conductor is the ratio of potential difference (V) across it and the current (I) that flows through it
Resistance = potential difference / current
resistance is measured in Ohm (Ω)
determining the resistance
a voltmeter is connected across the conductor to measure the potential difference
an ammeter is connected in series with conductor to measure current
factors affecting resistance
length of wire: longer the wire, higher the resistance
cross-sectinal area: wider the total surface area, lower the resistance
type of material: copper wire have lower resistance
temperature: higher the temperature, higher the resistance
resistance of a piece of wire is:
directly proportional to its length
inversely proportional to its cross-sectional area
Danger of electricity
structure of three-pin plug
Link Title
clearer picture
earth wire: it is connected to the metal casing of the apliance. The earth wire conducts current to the Earth when there is a leakage
fuse: whould blow when the current exceeds the rated value
neutral wire: enables current to flow back to the mains
live wire: brings electric current from the mains to the appliance
AC and DC
AC
AC (alternating current): flows backwards and forwards aroud 50 times per second
DC
DC (direct current ): only flows in one direction
Link Title
for a clearer picture
Magnetism
the closer the poles, the greater the force between them
like poles repel; unlike poles attract
magnetic field
