What is meant by latent heat? heat required to change state (without changing its temperature) Name an instrument used to measure temperature - Leaving Cert Physics - Question 9 - 2016

A thermometer is used to measure temperature.

To calculate the energy removed, use the formula:

$Q = mc\Delta T$

where:

• $m = 0.75 \, kg$
• $c = 4200 \, J \, kg^{-1} \, K^{-1}$ (specific heat capacity of water)
• $\Delta T = 20 - 0 = 20 \, K$ (change in temperature)

Thus, the energy removed is:

$Q = 0.75 \times 4200 \times 20 = 63000 \, J$

To calculate the energy removed during the phase change from water to ice, use:

$Q = mL_f$

where:

• $m = 0.75 \, kg$
• $L_f = 3.3 \times 10^5 \, J \, kg^{-1}$ (latent heat of fusion of water)

Thus, the energy removed is:

$Q = 0.75 \times 3.3 \times 10^5 = 247500 \, J$

To calculate the energy removed, use:

$Q = mc\Delta T$

where:

• $m = 0.75 \, kg$
• $c = 2200 \, J \, kg^{-1} \, K^{-1}$ (specific heat capacity of ice)
• $\Delta T = 0 - (-15) = 15 \, K$

Thus, the energy removed is:

$Q = 0.75 \times 2200 \times 15 = 24750 \, J$

Using the power rating of the freezer, we can find the time taken:

$P = \frac{E}{t} \Rightarrow t = \frac{E}{P}$

where:

• $E = 9000 \, J$
• $P = 300 \, W$

Thus, the time taken is:

$t = \frac{9000}{300} = 30 \, s$

As water freezes, it expands. This expansion can create pressure inside the glass bottle. If the pressure exceeds the strength of the glass, it leads to cracking and shattering.

A heat pump operates by extracting heat from a colder environment and transferring it to a warmer environment. It does this using a refrigerant that evaporates and absorbs heat from the cold space, then compresses it to release heat into the warmer space.

1. The refrigerant evaporates in the evaporator, absorbing heat.
2. The vapor is compressed, raising its temperature.
3. The high-temperature vapor releases heat in the condenser.
4. The refrigerant returns to a liquid state and repeats the cycle.