Physics 5054 · O Level · Specific heat capacity

Specific heat capacity — practice question

A student uses an electrical method to obtain an approximate value for the specific heat capacity of water. The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1 g of the substance by $1\,^{\circ}\text{C}$. He arranges the apparatus as shown in Fig. 1.1. He pours a mass $m$ of water into a beaker, with $m = 100\,\text{g}$. He puts a heater into the water in the beaker. He attaches a voltmeter so that it measures the potential difference across the heater. The student measures the water’s starting temperature and notes it at time $t = 0$ in Table 1.1. He closes the switch, starts a stopwatch and measures the temperature $\theta$ of the water every $60\,\text{s}$ for $6\,\text{minutes}$. He records the current $I$ in the heater and the potential difference $V$ across the heater. His readings are: $I = 4.0\,\text{A}$ and $V = 14.8\,\text{V}$. He opens the switch.
(a)[1]

Add a voltmeter symbol to the circuit diagram in Fig. 1.1 to indicate that the potential difference across the heater is being measured.

(b(i))[1]

The thermometer reading at time $t = 240\,\text{s}$ is shown in Fig. 1.2. Read the thermometer and write the temperature in Table 1.1.

(b(ii))[2]

State why it is important to: 1. make sure that the heating coil is completely immersed in the water 2. stir the water before taking each temperature reading.

(c(i))[4]

On the grid in Fig. 1.3, plot $\theta/^{\circ}\text{C}$ on the y-axis against $t/\text{s}$ on the x-axis. Begin the temperature axis at $20\,^{\circ}\text{C}$. Draw the smooth curve of best fit.

(c(ii))[2]

Use your graph to calculate the rise in temperature $\Delta \theta$ of the water during the first $200\,\text{s}$ of heating.

(d(i))[1]

Calculate the thermal energy $E$ delivered by the heater in the first $200\,\text{s}$ and state the unit. Use the equation given: $E = V \times I \times t$.

(d(ii))[2]

Calculate a value for the specific heat capacity $c$ of water. Use the mass given at the start of this question, your answers to (c)(ii) and (d)(i), and the equation: $E = m \times c \times \Delta \theta$.

(e(i))[1]

The specific heat capacity of water is $4.2\,\text{J g}^{-1}\,^{\circ}\text{C}^{-1}$. Look at the apparatus arrangement shown in Fig. 1.1. Suggest one practical reason why your calculated value of $c$ is not accurate.

(e(ii))[1]

State one improvement to the apparatus that would lead to a more accurate result.

(f)[1]

Another student repeats the experiment but does not switch off the heater at the end. The water temperature keeps rising until it reaches $82\,^{\circ}\text{C}$ and then stays at that value. Suggest one reason why the temperature of the water stops increasing when it reaches $82\,^{\circ}\text{C}$.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme.

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI