Electricity (Chapters 16-22) Done by: Nathaniel Seah (23) 4Eng

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Electricity (Chapters 16-22) Done by: Nathaniel Seah (23) 4Eng by Mind Map: Electricity (Chapters 16-22) Done by: Nathaniel Seah (23) 4Eng

1. Electromagnetism

1.1. Magnetic Field around a straight line wire

1.1.1. Magnetic field is stronger in the region around the wire

1.1.2. Magnetic Field is weaker when further away from the wire

1.1.3. When the magnitude of the current flowing through the wire is increased, more magnetic field lines will be formed indicating a stronger field

1.1.4. When current is reversed, the direction of the magnetic field will also increase

1.2. Right hand grip rule

1.2.1. Thumb = direction of current

1.2.2. Fingers curl = direction of the magnetic field

1.3. Magnetic current of a flat coil

1.3.1. Magnetic field due to current in a flat coil is stronger inside the coil. Because fields from each part of the wire are in the same direction and are confined to a small area

1.4. Magnetic field of a solenoid

1.4.1. Magnetic field can be increased by Increasing the magnitude of the current Increasing the number of turns around the solenoid Inserting a soft iron core into the solenoid

1.5. Fleming's left hand grip rule

1.5.1. Can be applied to all moving charges

1.6. Forces between two parallel, current-carrying conductors

1.6.1. Conductors with currents flowing in the same direction attract

1.6.2. Conductors with currents flowing in the opposite directions repel

1.7. D.C motor

1.7.1. Turning effects can be increased by...

2. Static Electricity

2.1. Charging

2.1.1. Induction Production of electric charge on the surface of a conductor due to the influence of an electric field Can be done over and over again Aim is to get either a positive or negative charge Earthling process Charging by induction

2.1.2. Rubbing Transferring charges from one object to another

2.2. Materials

2.2.1. Negative charge Amber rubbed with fur Rubber rubbed with fur Polythene rubbed with wool

2.2.2. Positive charge Glass rubbed with silk Perspex rubbed with wool

2.2.3. Charge does not flow in electrical insulations

2.2.4. Electrical conductore allow charge to flow throught them.Metals are good electrical conductors

2.3. Applications

2.3.1. Photocopier

2.3.2. Laser printer

2.4. Drawing Field Lines

2.4.1. Line begins from positive charge and ends on negative charge

2.4.2. Lines drawn leaving a positive charge or ending on a negative charge are proportional to the magnitude of the charge


2.5. van de Graff generator

2.6. Charges

2.6.1. Not necessarily due to friction but by contact

2.6.2. Measured in Coulomb (C)

2.6.3. Region in which and electric charge experiences a charge Experience weaker charges when placed further apart

2.6.4. Law of electrostatics Like charges repel Unlike charges attract

2.6.5. Positive,negative and neutral charges Positive Charge Electric field lines point outwards Positively charged if there are more positive charges than negative charges on the object Negative Charge Electric field lines point inwards Negatively charged if there are more negative charges than positive charges on the object The object is neutral if there are equal numbers of positive and negative charges on the object Strength Nearer Furthur

3. Current of Electricity

3.1. Current

3.1.1. Rate of flow of Charge

3.1.2. Q= It Charge = Current × time

3.1.3. SI unit is coulomb per second (C/s) or ampere (A)

3.1.4. Conventional Current Direction a positive charge will flow Protons move from + to -

3.1.5. Motion of Electrons Direction a negative charge will flow Electrons move from - to +

3.1.6. Measured using an ammeter Must be connected in series to the circuit Measure the same current throughout as the same current flows through the simple circuit

3.2. Electromotive Force (e.m.f)

3.2.1. The work done by the electrical source in driving a unit charge around a complete circuit

3.2.2. Electromotive force= work done/charge

3.2.3. SI unit is joule per coulomb (J/C) or volt (V)

3.2.4. Series Connection gives an increased e.m.f because charges gain potential energy from all the cells they pass through. eg. 1.5+1.5+1.5=4.5

3.2.5. Parallel Charges flowing around the circuit splits into 3 equal portions Gain in potential energy for any charge in each portion is only from one of the three cells Advantages The cells last longer before going flat the cells are able to supply a larger current

3.3. Potential difference

3.3.1. Work done to drive a unit charge through the component

3.3.2. Potential difference=Work done/charge

3.3.3. SI unit is joule per coulomb (J/C) or volt (V)

3.3.4. Measured by a voltmeter Connected in parallel to the component Total energy gained =total energy lost.

3.3.5. Sum of all the e.m.f.s of the cells must be equal to the sum of potential differences across all the components in the circuit

3.4. Resistance

3.4.1. The ratio of the potential difference across the component to the current flowing through it

3.4.2. R = V/I

3.4.3. SI unit is Ω

3.4.4. Factors affecting resistance Length A long wire has more resistance than a short wire Area A thin wire has more resistance than a thick wire Temperature Conductors Semi-conductors R=pl/A p= resistivity l= length A= area

3.4.5. Ohm's Law Current through a metal conductor is directly proportional to the potential difference across the ends of the conductor provided that the physical condition and temperature remain constany V/I= constant

3.5. Series

3.5.1. Formulas I =I1=I2=I3 Current at every point in the circuit is the same V= V1+V2+V3 The component with the largest resistance has the highest potential difference across it R= R1 + R2 + R3

3.5.2. Advantages Higher voltage

3.5.3. Disadvantages The current will cease to flow if there is a break in the circuit Smaller battery life

3.6. Parallel

3.6.1. Formulas I= I1 + I2 + I3 V= V1=V2=V3 (1/R) = (1/R1) + (1/R2) + (1/R3) Component with the smallest resistance has the highest current flowing through it

3.6.2. Advantages Any breaks in the circuit does not affect the current flow in the other branches of the circuit Longer battery life

3.6.3. Disadvantages Lower voltage

3.7. Resistors

3.7.1. Variable Resistor V1=R1/(R1+R2)X V Potential divider circuit Cannot reduce current and potential difference to zero Potentiometer Can reduce current and potential difference to zero

3.7.2. Transducers Output transducer Converts electrical energy into other forms of energy Input transducer Changes non-electrical energy into electrical energy Thermistors Light-dependent resistors

3.8. Cathode-ray Oscilloscope

3.8.1. Uses Measure a.c and d.c voltages Displaying wave forms Measures time and frequency speed of sound

3.8.2. axis y-axis voltage x-axis time

4. Magnetism

4.1. Law of Magnetism

4.1.1. Like Poles Repel, Unlike Poles Attract

4.2. Properties

4.2.1. Found in magnetic materials Metals

4.2.2. Not found in non-magnetic materials Plastics Fabrics Wood

4.3. Induced magnetism

4.3.1. eg. a single bar magnet can attract a iron nail hence becoming a magnet. In turn attracting another nail. When the bar magnet is removed,Both the nails fall off due to the lost of their induced magnetism.

4.4. Magnetic Materials

4.4.1. May Undergo Magnetisaton Stroking Take one permenant magnet and stroke a magnetic material lenghtwise. Stroke from end to end over 20 continuous strokes Using Direct Current A steel bar is inserted into a solenoid and a direct current is made to flow through the solenoid. A strong magnetic current is produced by the solenoid leading to the steel bar becoming magnetised.

4.4.2. May Undergo Demagnetisation Heating magnet must lie in an east-west direction Hammering magnet must lie in an east-west direction and heated till red-hot then cooled

4.4.3. Magnets Permanent Magnet Steel Uses Temporary Magnet Iron Electromagnets

4.5. Applications

4.5.1. Compass Discovered by the ancient Chinese in 2000BC A magnet 2 Poles North pole South pole Similar to a bar magnet

4.6. Bar magnet(1)

4.6.1. with... Bar magnet (2) North pole of 1 attracts south pole of 2 North pole of 1 repels north pole of 2 soft iron rod (magnetic material) (2) North pole of 2 can be attracted by either poles of 1 a non-magnetic material (wood) (2) 1 and 2 remain stationary

4.6.2. Strength Peak strength is not at the poles but is around 0.5cm away from the poles.

4.7. Field Lines

4.7.1. Drawing magnetic field lines Things required Pencil Paper Compass Bar magnet how to... Put the bar magnet on the sheet of paper, and trace out its shape Make a dot at the edge of a pole Put the end of the compass on top of the dot and make a dot at where the needle points. Repeat Steps 1-3 till the dots reach either the end of the paper or the other pole Draw a line to connect the dots. Yay you've got your first field line :) When finished, pick another spot near the magnet and repeat steps 1-5 for more field lines

4.7.2. Properties Lines start from the north pole and end at either the south pole or simply away from the north pole The lines cannot overlap or cross each other The lines are closer to each other in a stronger magnetic field

5. Practical electricity

5.1. Heating Elements

5.1.1. Nichrome High resistivity High melting points

5.2. Calculations and Formulas

5.2.1. Calculation of Electrical energy Enrgy = Charge x potential difference E = QV E = VIt E= I²RT E = (V²/R)t Measuring Electricity consumption Energy released = Power x time

5.2.2. Calculation of electrical power Power = Energy released/Time taken P = E/t P = VI = I²R = V²/R SI unit is the watt 1 watt (W) = 1 joule per second (J/s) 1 milliwatt (mW) = 1/1000 W 1 kilowatt (kW) = 1000W 1 megawatt (MW) = 1 000 000 W

5.3. Dangers

5.3.1. Damaged insulation Exposed live wires may cause an electric shock if someone touches it May also cause a short circuit Which may eventually lead to a fire

5.3.2. Overheating of cables Thin wires = higher resistance = more heat Use of multi-way adaptors If used at the same time, total current drawn through the cables from the main supply may be too large that the cable becomes overloaded and overheated. This may result in a fire Weight of the many plugs on an adaptor may pull it partly out of the socket, revealing live prongs which may result in a bad connection or an electric shock if someone touches it. Damp conditions Dry skin = Higher resistance approx.100 000 ohms Wet skin = low resistance approx a few hundred ohms

5.4. Safety

5.4.1. Fuses Placed on the live wire Melts and breaks when the current exceeds a certain value causing an open circuit Protects the appliance Protects us Must take a current which is slightly larger than the maximum current that is allowed to pass through Fuses will not melt prematurely

5.4.2. Switches Placed on the live wire Used as a safety device to cut off the flow of the current when someone accidentally touches a live wire

5.4.3. Earth wire Joined to the metal case of an appliance. If the live wire accidentally touches the case, the current will flow to the earth and blow the fuse in the live wire. The case is prevented from being live and the person avoids getting an electric shock

5.4.4. Double insulation Casing is made of plasic Electrical parts can never come into contact with the outer casing of the device.

5.5. Three pin plug

5.5.1. Live wire = brown

5.5.2. Neutral wire = blue

5.5.3. Earth wire = yellow and green stripes Longest pin. Open safety shutters that cover the slots for the earth and neutral pins Ensures that the appliance is properly earthed before a current flows through