Electricity
9th Grade Science · 7 lessons
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Lessons in this unit
- 1Charge, Current and the CoulombElectric current is the rate of flow of charge: I = Q/t, measured in amperes. One ampere is one coulomb of charge passing a point each second. In a metal the carriers are free electrons, drifting slowly even though the signal travels almost instantly.Experiment
- 2Potential Difference and the VoltPotential difference is the energy transferred per unit charge, V = E/Q, measured in volts. A 12 V supply gives each coulomb 12 joules. Voltmeters are connected in parallel across a component because they compare energy at two points.Experiment
- 3Resistance and Ohm's LawResistance is potential difference divided by current, R = V/I, in ohms. For a metallic conductor at constant temperature, current is proportional to potential difference — Ohm's law. Heat the wire and the line curves, because resistance rises with temperature.Experiment
- 4Series and Parallel CircuitsIn series the same current passes through every component and potential differences add. In parallel each branch has the full supply potential difference and the branch currents add. That is why household lighting is wired in parallel — one failed lamp leaves the rest lit.Experiment
- 5Electrical Power and Energy CostElectrical power is P = VI, and also I²R. Energy used is power times time, and household bills are charged in kilowatt-hours: one kilowatt running for one hour. A 2 kW heater run for three hours uses 6 kWh.Experiment
- 6Static ElectricityRubbing two insulators transfers electrons, leaving one negative and the other positive. Like charges repel and unlike attract. A charged object attracts neutral ones by induction, which is how a rubbed balloon sticks to a wall.Experiment
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