Presentation on theme: "S.MORRIS 2006 Electricity and Magnetism More free powerpoints at www.worldofteaching.com All you need to be an inventor is a good imagination and a pile."— Presentation transcript:
S.MORRIS 2006 Electricity and Magnetism More free powerpoints at www.worldofteaching.com All you need to be an inventor is a good imagination and a pile of junk. -Thomas Edison
Electricity – electrons moving through a metal wire.
The CELL The cell stores chemical energy and transfers it to electrical energy when a circuit is connected. An example of a cell is a Battery. The cell’s chemical energy is used up pushing a current around a circuit.
What is an electric current? An electric current is a flow of microscopic particles called electrons flowing through wires and components. + - In which direction does the current flow? By convention (thanks to Ben Franklin) - from the Negative terminal to the Positive terminal of a cell. (Electrons actually move in the opposite direction, from the negative terminal to the positive one.)
simple circuits Here is a simple electric circuit. It has a cell, a lamp and a switch. To make the circuit, these components are connected together with metal connecting wires. cell lamp switch wires
simple circuits When the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around. If there were any breaks in the circuit, the current could not flow.
circuit safety If you connect a wire between the two terminals, the electrons will flow from the negative end to the positive end as fast as they can. This will quickly wear out the battery and can also be dangerous To properly harness the electric charge produced by a battery, you must connect it to a load. The load might be something like a light bulb, a motor, a resistor or an electronic circuit like a radio.
circuit diagram cellswitchlampwires Scientists usually draw electric circuits using symbols;
circuit diagrams In circuit diagrams components are represented by the following symbols; cell or battery switchlamp motor ammeter voltmeter buzzer resistorvariable resistor generic resistor
types of circuit There are two types of electrical circuits; SERIES CIRCUITSPARALLEL CIRCUITS
The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. SERIES CIRCUITS If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.
PARALLEL CIRCUITS The current has a choice of routes. The components are connected side by side. If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.
Ohm’s Law I = V / R Georg Simon Ohm (1787-1854) I = Current (Amperes) (amps) V = Voltage (Volts) R = Resistance (ohms)
How you should be thinking about electric circuits: Voltage: a force that pushes the current through the circuit (in this picture it would be equivalent to gravity)
Resistance: friction that impedes flow of current through the circuit (rocks in the river) How you should be thinking about electric circuits:
Current: the actual “substance” that is flowing through the wires of the circuit (electrons!) How you should be thinking about electric circuits:
measuring current Electric current is measured in amps (A) using an ammeter connected in series in the circuit. A
measuring current A A This is how we draw an ammeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT
measuring current SERIES CIRCUIT PARALLEL CIRCUIT current is the same at all points in the circuit. 2A current is shared between the components 2A 1A
copy the following circuits and fill in the missing ammeter readings. ? ? 4A 3A? ? 1A ? 3A 1A
measuring voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter V
Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current. measuring voltage Unlike an ammeter a voltmeter is connected across the components Scientist usually use the term Potential Difference (pd) when they talk about voltage.
measuring voltage V This is how we draw a voltmeter in a circuit. SERIES CIRCUITPARALLEL CIRCUIT V
series circuit 1.5V voltage is shared between the components 1.5V 3V
voltage is the same in all parts of the circuit. 3V parallel circuit 3V
measuring current & voltage copy the following circuits on the next two slides. complete the missing current and voltage readings. remember the rules for current and voltage in series and parallel circuits.
What is Magnetism? Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.
Atoms themselves have magnetic properties due to the spin of the atom’s electrons. These areas of atoms are called “domains” Groups of atoms join so that their magnetic fields are all going in the same direction
When an unmagnetized substance is placed in a magnetic field, the substance can become magnetized. This happens when the spinning electrons line up in the same direction.
While a magnetized substance looks like this… Iron Lodestone (Magnetite)
Which of the metals below are magnetic metals? aluminium (Al) silver (Ag) iron (Fe) gold (Au) nickel (Ni) cobalt (Co) copper (Cu) zinc (Zn) magnesium (Mg) Magnetic materials
N S Al Zn Ag Cu Au Mg Fe Ni Co A magnetic material is attracted to a magnet. Magnetic materials Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic.
ELECTRICITY MAGNETISM How can you tell? Compass needle moves when near electrical current - creating an magnetic field Electric currents cause magnetism
MAGNETISM ELECTRICITY How can you tell? Electromagnetic induction moving a magnet in and out of a coiled wire created an electrical current without a battery A moving magnet can generate electricity
Magnets have two ends, usually marked "north" and “south“ Magnets attract things made of steel or iron Fundamental law of all magnets: Opposites attract and likes repel. An electromagnet works in the same way, except it is "temporary" the magnetic field only exists when electric current is flowing. An Electromagnet
This magnet is able to pick up small steel things like paper clips, staples and tacks. Simple electromagnet
Strength of Electromagnets Depends on three main things: Number of turns in the coil –The more turns in a coil, the stronger the magnet Amount of current in the coil –If the voltage is increased, so will the current, which will increase the strength of the magnetic field