Root-mean-square current and voltage

• Young Digital Planet
• Key Stage 4
• Physics
• XII. Alternating current
• 62. Alternating current and a generator

• Exam Specifications
• Key Stage 4
• AQA GCSE Physics (4451)
• III. Physics 1a
• 12. Why are electrical devices so useful?
• Examples of energy transformations that everyday electrical devices are designed to bring about.
• Examples of everyday electrical devices designed to bring about particular energy transformations.
• V. Physics 2
• 23. What is mains electricity and how can it be used safely?
• to compare potential differences of d.c. supplies and the peak potential differences of a.c. supplies from diagrams of oscilloscope traces
• An alternating current (a.c.) is one which is constantly changing direction. Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz).
• VI. Physics 3
• 34. How do generators work?
• to explain from a diagram how an a.c. generator works, including the purpose of the slip rings and brushes.
• If an electrical conductor ‘cuts’ through magnetic field lines, an electrical potential difference is induced across the ends of the conductor.
• If a magnet is moved into a coil of wire, an electrical potential difference is induced across the ends of the coil.
• If the wire is part of a complete circuit, a current is induced in the wire.
• If the direction of motion, or the polarity of the magnet, is reversed, the direction of the induced potential difference and the induced current is reversed.
• The generator effect also occurs if the magnetic field is stationary and the coil is moved.
• The size of the induced potential difference increases when: − the speed of the movement increases − the strength of the magnetic field increases − the number of turns on the coil increases − the area of the coil is greater.
• AQA GCSE Science A (4461) Physics
• I. Physics 1a Energy and Electricity
• 3. Why are electrical devices so useful?
• to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application
• to calculate the amount of energy transferred from the mains using: energy transferred = power × time (kilowatt-hour, kWh) = (kilowatt, kW) × (hour, h)
• to calculate the cost of energy transferred from the mains using: total cost = number of kilowatt-hours cost per kilowatt-hour
• Examples of energy transformations that everyday electrical devices are designed to bring about.
• Examples of everyday electrical devices designed to bring about particular energy transformations.
• The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which the device transforms energy.
• The power of an appliance is measured in watts (W) or kilowatts (kW).
• Energy is normally measured in joules (J).
• Electricity is transferred from power station to consumers along the National Grid.
• The uses of step-up and step-down transformers in the National Grid.
• AQA GCSE Physics (4451)
• I. Physics 2
• 7. What is mains electricity and how can it be used safely?
• to compare potential differences of d.c. supplies and the peak potential differences of a.c. supplies from diagrams of oscilloscope traces
• An alternating current (a.c.) is one which is constantly changing direction. Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz).

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