IGCSE Physics-Heat and Energy

A gas syringe contains air and tiny suspended dust particles in it. Explain why the dust particles do not settle to the bottom and remian suspended in the air.

The dust particles are under rapid, continuous and RANDOM molecular 'bombardment' by the HIGH ENERGY air molecules in the syringe. The direction in which air molecules will collide with the dust is COMPLETELY RANDOM, thus the dust molecules stay in the air.

How would you prove that an radioisotope only emmits alpha radiation. Explain why it proves that it only emmits alpha radiation.

1.) Take readings without the source to determine the background radiation count. 2.) Take readings of the radioiosotope placed directly infront of the G-M tube (less than 1 cm disance) 3.) Now cover the the radioisotope in one layer of thick paper/thin cardboard. 4.) The readings with the paper brought to the G-M tube at the same distance should be the same as th background radiation count. This works becuase alpha particles are completly absorbed by thin cardboard while beta and gamma would easily pass through it, therefore if an isotope only emmits alpha radiation Then no ionising radiation FROM THE SOURCE would be pick up by the G-M tube therefore would have the same readng as the background radiation count.

What does it mean when something is said to tbe 100% efficient

All of energy input = USEFUL energy output. No energy is lost as heat or sound etc.

Explain how a thermocouple is used to measure temperature.

One junction is placed in the temperature we want to measure and the other at room temperature. The difference in temperature between the two junctions creates a potential difference across the thermocouple. When the circuit is completed and connected to a Galvinometer which measures the current driven by the potential difference created by the temperature difference.