Distinguish between heat and temperature - Leaving Cert Physics - Question 9 - 2015

The power of the kettle element is given as 0.8 kW. To find the energy supplied per second, we convert kW to watts (1 kW = 1000 W):

$P = 0.8 ext{ kW} = 800 ext{ W}$

Since 1 W = 1 J/s, the energy supplied by the element per second is:

$800 ext{ J/s}$

To find the time taken to heat the water, we can use the formula:

$t = \frac{Q}{P}$

Where:

• $t$ is the time in seconds
• $Q$ is the heat energy (found in part (i), $167200 ext{ J}$)
• $P$ is the power (in watts, $800 ext{ W}$)

Substituting the values:

$t = \frac{167200}{800} = 209 ext{ seconds}$

Plastic is a poor conductor of heat, which makes it a good material for kettle handles. This prevents burns and allows users to handle the kettle safely when it's hot.

Heat is transferred throughout the liquid in the kettle mainly through convection. As the water at the bottom heats up, it becomes less dense and rises, while cooler, denser water descends to take its place, creating a convection current.

The heating element of a kettle is made of metal because metals are good conductors of heat. This allows for efficient heat transfer from the element to the water.

The heat source is placed at the bottom to promote efficient convection. As the water at the bottom heats up and rises, it allows cooler water to flow downwards, ensuring uniform heating throughout the kettle.