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QLDPhysicsQuick questions
Unit 1: Thermal, nuclear and electrical physics
Quick questions on Electrical power and energy (QCE Physics Unit 1)
7short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is confusing power with energy?Show answer
A $100$ W bulb has a power rating. To get energy used, multiply by the time. The same $100$ W bulb running $1$ h uses $360\,000$ J; running $10$ h uses $3.6 \times 10^6$ J.
What is mixing watts and kilowatts?Show answer
A $2400$ W kettle is $2.4$ kW, not $2400$ kW. Convert at the start.
What is using the wrong power formula for non-ohmic devices?Show answer
$P = VI$ always works. $P = I^2 R$ and $P = V^2 / R$ assume Ohm's law holds. For a diode or a lamp at high current, use $P = VI$ from measured operating values.
What is forgetting the factor of $3600$ in kWh to joule conversion?Show answer
$1$ kWh $= 3.6 \times 10^6$ J, not $3600$ J.
What is iA1?Show answer
Often an oscilloscope or data-logger trace with $V$ and $I$ measured, asking for instantaneous and average power.
What is eA Paper 1?Show answer
Multiple choice on which power formula is appropriate, and conversions between watts and kilowatt-hours.
What is eA Paper 2?Show answer
Combined with the series-and-parallel dot point to find the power dissipated in each individual resistor of a small circuit, then total energy delivered by the battery over a stated time.
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