POWER ON ELEC APPLIANCES, N GRID, ELEC FIELDS, STATIC ELEC

• How is energy transferred by electrical appliances?

  Energy is transferred electrically by electrical appliances.
• What happens when a moving charge transfers energy?

  The charge does work against the resistance of the circuit.
• What is the relationship between work done and energy transferred when a current flows?

  Work done is the same as energy transferred when a current flows.
• What do electrical appliances do in a circuit?

  They are designed to transfer energy to components in the circuit.
• How do kettles transfer energy?

  Kettles transfer energy from the mains energy supply to the heating element.
• How does a handheld fan transfer energy?

  Energy is transferred from the battery to the kinetic energy store of the fan's motor.
• What happens to energy transfer as the current increases in an appliance?

  More energy is transferred to the thermal energy stores of the components.
• How can you calculate the efficiency of an electrical appliance?

  
  

  useful power output / useful power input
• What factors determine the total energy transferred by an appliance?

  The total energy transferred depends on how long the appliance is on and its power.
• What is the definition of power in relation to an appliance?

  Power is the energy that an appliance transfers per second.
• What is the formula for calculating energy transferred by electrical work?

  Energy transferred (J) = Power (W) × Time (s) or $E =$$Pt$.
• If a 600 W microwave is used for 5 minutes, how much energy is transferred?

  The energy transferred is $E =$$600 \times (5 \times 60) =$$180000 \text{ J}$.
• What does the power rating of an appliance indicate?

  The power rating indicates the maximum amount of energy transferred per second when the appliance is in use.
• How does a higher power rating affect electricity usage?

  A higher power rating means more electricity is used in a given time, making it more expensive to run.
• Can a more powerful appliance be less efficient? Why?

  Yes, a more powerful appliance may be less efficient and transfer the same or less energy to useful stores.
• What is the formula for potential difference in relation to energy transferred?

  The formula is $E =$$QV$, where E is energy, Q is charge flow, and V is potential difference.
• What does a higher potential difference from a battery do?

  A higher potential difference supplies more energy to the circuit for every coulomb of charge that flows.
• How much energy is transferred by a 3 V battery with 140 C of charge passing through it?

  The energy transferred is $E =$$140 \times 3 =$$420 \text{ J}$.
• How can power also be calculated in relation to current and potential difference?

  Power can be calculated using the formula $P =$$VI$, where P is power, V is potential difference, and I is current.
• How do you calculate the current through a 1.0 kW hair dryer connected to a 230 V supply?

  Current is calculated as $I =$$P ÷ V =$$1000 ÷ 230 \approx 4.3 \text{ A}$.
• What is the purpose of transformers in the national grid?

  Transformers change the potential difference for efficient transmission of electricity.
• How does a step-up transformer work?

  A step-up transformer has more turns on the secondary coil than the primary coil, increasing the potential difference.
• What happens to the current when the potential difference is increased by a transformer?

  The current decreases when the potential difference is increased.
• What is the function of a step-down transformer?

  A step-down transformer reduces the potential difference and increases the current at the local consumer end.
• How is power conserved in transformers?

  The power in the primary coil equals the power in the secondary coil, as transformers are nearly 100% efficient.
• What is static electricity?

  Static electricity involves charges that are not free to move, often building up in one place.
• What causes the build-up of static electricity?

  The build-up of static electricity is caused by friction.
• How is an electric field created?

  An electric field is created around any electrically charged object.
• How does the strength of an electric field change with distance?

  The strength of the electric field decreases as you move further away from the charged object.
• How can electric fields be represented visually?

  Electric fields can be shown using field lines that go from positive to negative.
• What happens to charged objects in an electric field?

  Charged objects feel a force when placed in the electric field of another object.
• How does distance affect the force between charged objects?

  As the distance between charged objects increases, the strength of the field and the force between them decreases.
• What causes sparks in terms of electric fields?

  Sparks occur when there is a high enough potential difference between a charged object and the earth.
• What happens to air particles during sparking?

  A strong electric field causes electrons in air particles to be removed, leading to ionisation.
• How does ionisation affect air's conductivity?

  Ionisation makes air much more conductive, allowing a current to flow through it.
• What is the basic definition of a circuit?

  A circuit is a closed loop that allows current to flow.
• What is the role of a power station in the national grid?

  A power station generates electricity for distribution via the national grid.
• How does the national grid ensure electricity is available when needed?

  The national grid allows power stations to switch to spare stations if one is out of order.
• What factors influence electricity demand throughout the day?

  Electricity demand changes with daily activities, such as when people come home or when it gets darker.
• How do power stations manage unexpected shutdowns?

  Power stations run below maximum output to have spare capacity for high demand or unexpected shutdowns.