OCR A-Level Physics B H557
Planning
Implementing
Analysis
Evaluation
Practical Skills
Use of Apparatus and Techniques
Fundamental Data Analysis
Imaging and Signalling
Sensing
Mechanical Properties of Materials
Waves and Quantum Behaviour
Space, Time and Motion
Creating Models
Out Into Space
Our Place in the Universe
Matter: Very Simple
Matter: Hot or Cold
Electromagnetism
Charge and Field
Probing Deep Into Matter
Ionising Radiation and Risk
Matter: Very Simple
Finding specific thermal capacity by an electrical method
- 3 things to know
- Components 01, 02 and 03
Overview
Recall questions on the readings that give the energy supplied, oil in the holes and lagging, whether heat loss is random or systematic, cooling corrections, and adapting the method to a liquid.
What you need to know
Answer each one before you reveal it.
Which three electrical measurements give the energy delivered by an immersion heater?
Why is a little oil put into the thermometer and heater holes of the block?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Describe how an electrical method is used to find the specific thermal capacity of a metal block.
Model answer
An immersion heater and a thermometer are fitted into holes in a lagged block of known mass, the heater is run for a measured time at a measured potential difference and current, and the temperature rise is recorded.
- 2
Which three electrical measurements give the energy delivered by an immersion heater?
Model answer
The potential difference across it, the current through it and the time for which it runs, since the energy supplied is VIt.
- 3
How is the specific thermal capacity calculated from the readings of an electrical experiment?
Model answer
It is the electrical energy supplied divided by the mass and the temperature rise, c = VIt ÷ (mΔθ).
- 4
A 1.0 kg block is heated for 300 s by a heater carrying 4.0 A at 12 V and its temperature rises by 16 K. Calculate the specific thermal capacity.
Model answer
c = (12 × 4.0 × 300) ÷ (1.0 × 16) = 900 J kg⁻¹ K⁻¹.
- 5
Why is a little oil put into the thermometer and heater holes of the block?
Model answer
The oil improves thermal contact so the heater and thermometer take up the temperature of the metal quickly.
- 6
Why is the block lagged?
Model answer
Lagging cuts the energy escaping to the surroundings, so more of the energy supplied goes into raising the temperature of the block.
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