A tiny thermal micro-actuator in a medical implant is activated by passing an electric current through a thin indium wire, causing it to melt and release a spring.
The indium wire melts when a charge flow of 4.5 C4.5\text{ C}4.5 C passes through it in a time of 0.60 s0.60\text{ s}0.60 s. Calculate the current in the wire when it melts. Use the equation:
current=charge flowtime \text{current} = \frac{\text{charge flow}}{\text{time}} current=timecharge flowThe mass of the indium wire is 0.035 g0.035\text{ g}0.035 g and the specific latent heat of fusion of indium is 60,000 J/kg60{,}000\text{ J/kg}60,000 J/kg. Calculate the thermal energy needed to melt the wire. Use the equation:
energy=mass×specific latent heat \text{energy} = \text{mass} \times \text{specific latent heat} energy=mass×specific latent heatThe micro-actuator transfers some energy to its surroundings as it heats up and melts. How does transferring energy to the surroundings affect the total energy that must be supplied to melt the indium wire?
37 exam-style questions on AQA GCSE Physics 3.2 Internal energy and energy transfers, covering 3.2.1 Internal energy, 3.2.2 Temperature changes in a system and specific heat capacity, and 3.2.3 Changes of state and specific latent heat. Each one has a worked solution and a mark scheme showing where the marks go.