physics Flashcards
what does the earth wire do?
the earth wire a safety wire to stop the appliance becoming live. The potential difference of the Earth wire is 0 V. It only carries a current if there is a fault
what does the live wire do?
The live wire is dangerous because it has a high potential difference of 230V. This would cause a large current to flowthrough you if you touched it.
what does the neutral wire do
The neutral wire completes the circuit. It has a potential difference of 0 V.
what is the national grid
The National Grid is a nationwide network of cables and transformers that link power stations to homes, offices, and other consumers of mains electricity.
what are step up transformers
Step-up transformers are used to increase the potentialdifference from the power station to the transmission cables
what are step down transformers
Step-down transformers are used to decrease the potentialdifference from the transmission cables to the mains supply in homes and offices so that it is safe to use.
Why do transformers improve efficiency?
A high potential difference across the transmission cables means that a lower current is needed to transfer the same amount of power, since:power (W) = current (A) × potential difference (V)P = IV
Energy transfer in electrical appliances (equations)
You can calculate the charge flow using the equation:charge flow (C) = current (A) × time (s)Q = It
You can find the energy transferred to an electrical appliance when charge flows through it using:energy transferred (J) = charge flow (C) × potential difference (V)E = QV
You can find the energy transferred by an electrical appliance using the equation:energy transferred (J) = power (W) x time (s)
Why is the current provided by a cell called a direct current (d.c.)?
only flows in one direction
What is an alternating current (a.c.)?
current that repeatedly reverses direction
(supplys mains electricity)
What is the frequency and voltage of mains electricity?
50 Hz, 230 V
What colours are the live, neutral, and earth wires in a three-core cable?
live = brown, neutral = blue, earth = green and yellow stripes
What two things does energy transfer to an appliance depend on?
power of appliance, time it is switched on for
What are the units for power, current, potential difference, and resistance?
watts (W), amps (A), volts (V), ohms (Ω)
