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Electricity and Magnetism ISCI 2002

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1.Electricity is a Force – Vector – Electric charges (attract and repel) – Comb and Ball Example 2.Atoms – Protons and Electrons – “Atoms are electrically neutral” – Formation of ions Rub a rubber rod with fur 3.Insulators – Does not allow charge to run through it 4.Conductors – Allows for charges to run through it Metals

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Van de Graff Generator How it Works: Belt – high RPM Picks up charges Distributes charges to spherical dome surface Conductors – Charges concentrate (curvature of surface is greatest)

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1.Coulomb’s Law – The force between charges is proportional to the product of the charges and inversely proportional to the square of the distance between them. 2. Equation – F e = k (q 1 q 2 ) r2r2 3. Newton’s Universal Law of Gravitation Differences – Charges may be positive or negative (mass always positive) – Electrical force is greater than gravitational force (k > G) k = constant (9.0 x 10 9 ) q = charges r = distance between charges

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1.Charged objects creates an electrical field around itself (space around the object) 2.Electrical Fields exert a force on any object placed into the field. – Fields may be weak or strong 3. Represented by vector lines (field lines) 4. Direction – field lines point; magnitude – lines closest together 5. If: – Positive charge – move in direction of lines – Towards negative charged area – Negative charges pushed in opposite direction

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Lines point away from positive charges to negative charges All field lines begin at the positive charge More charge on an object, more field lines attached to it.

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1.If you separate the positive and negative charges from each other, WORK must be done! 2. This creates Electrical Potential Energy (EPE). – A charge in a field has energy – External force pushes it the against the field – work Creates EPE 3. If Charges are brought together again – Energy is released

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1.Work – Creates Electrical Potential Energy 2. How it is measured: – Electrical Potential = electric potential / charge 3. Unit – Volt – 1 Volt = 1 joule / charge (coulomb) – 1.5 – Volt Battery Gives 1.5 joules of energy to convert to 1 coulomb of charge flowing through a battery

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1.Electrical Conductor – Two electric potentials separated – Charges flow from one to the other 2.How a Chemical Battery Works – Removes electrons from one terminal and deposits them on another terminal Adds energy to the charge 3. Where does the energy come from? – Chemical reaction – breakdown (lead, zinc)

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1.Metals – Electrons (free) flow through the wires – Protons do not (bound to nuclei) 2.Non-Metals – Electrons and Protons both may flow – Car Battery

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1.Conductors – Diameter More narrow – greater resistance – Temperature Higher – more resistance – Material Metals (free electrons available) – Great Conductors! Rubber (no free electrons) – Poor Conductors or Insulators 2. Measured in Ohm’s (Ω) 3. Types of Current – AC vs DC

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1.Current and Voltage – Proportional relationship (Current = Voltage) 2.Current and Resistance – Current = 1/resistance 3.Ohm’s Law – Current = Voltage / Resistance I = current V = volts R = resistance

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1.Path of Electron Flow through wires 2. Simple 3. Series – Current flows through each lamp (resistor) – From positive terminal to negative terminal – Easy to make; Disadvantages? 4. Parallel – Electrical devices connected to the same two points of an electrical circuit – Three lamps Electrons travel to lamp one and return Video Link

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What type of Circuit is show at the Left? How do you know? What are the symbols used?

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1.Moving charges do work. 2. Rate at which work is done 3. Formula – Power = current x voltage 4.Unit – Watt

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1.Guess What? Magnetism is a force – vector 2.Where this force comes from – Metal atoms (Fe) – Domains – aligned atoms – Induced 3.Magnetic Fields – Space around a magnet – Magnetic Field – Field Lines – North pole to South Pole – Produced by moving electric charges – Video Link 1 Video Link 1 – Video Link 2 Video Link 2

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Electric Currents and Magnetic Fields A magnetic field is produced by the motion of electric charge. A magnetic field surrounding a current-carrying wire makes up a pattern of concentric circles.

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1.Magnetic Poles ------ Magnetic Forces 2. Like poles repel; unlike poles attract 3. Break a bar magnet – Still have a north and south pole

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1.Charges are moving – deflected by magnets 2.Particles moving through a wire are deflected – wire is also deflected 3.Electromagnetic Force – Electric Motors – Coil of wires turn - magnet – Current in motor – changes direction when coil makes a half-turn – Video Link Video Link 4. Meters – magnetic compasses detect electrical current – Compass in a coil of wire – current loop has effect on needle – Galvanometer (current); Voltmeter (V)

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