Experimental Contexts

Measure the room temperature $\theta_R$ and record it on the answer line.

$\theta_R$ = ______ $^\circ\text{C}$

Close the switch.

Record the potential difference across the thermistor $V_{XY}$ while the thermistor is at room temperature $\theta_R$ in Table 2.1 on page 6.

Open the switch.

Disconnect the voltmeter from points X and Y.

Reconnect the voltmeter across the 220 $\Omega$ resistor between points Y and Z.

Close the switch.

Record the potential difference across the 220 $\Omega$ resistor $V_{YZ}$ while the thermistor is at room temperature $\theta_R$ in Table 2.1 on page 6.

Open the switch.

Disconnect the voltmeter from points Y and Z.

Reconnect the voltmeter across points X and Y.

Ask your supervisor to pour hot water into the beaker until it is about half full.

Carefully place the thermometer in the hot water and stir the water gently.

Wait for about 30 s.

Measure the temperature of the hot water $\theta_H$ and record it on the answer line.

$\theta_H$ = ______ $^\circ\text{C}$

Close the switch.

Record the new potential difference $V_{XY}$ while the thermistor is at the temperature of the hot water $\theta_H$ in the bottom row of Table 2.1.

Open the switch.

Disconnect the voltmeter from points X and Y.

Reconnect the voltmeter across the 220 $\Omega$ resistor between points Y and Z.

Close the switch.

Record the new potential difference $V_{YZ}$ while the thermistor is at the temperature of the hot water $\theta_H$ in the bottom row of Table 2.1.

Open the switch.

Hold the thermistor by its connecting leads and carefully remove it from the hot water. Place it on the bench away from the rest of the circuit.

Explain why you waited for 30 s before measuring the temperature of the hot water.

Explain why you stirred the water before reading the temperature of the hot water.

The current $I$ in the circuit is calculated using the equation

where $R = 220\ \Omega$.

Use your measurements recorded in Table 2.1 to calculate the current $I$ at room temperature $\theta_R$ and at the temperature of the hot water $\theta_H$.

Record your answers in Table 2.1.

The resistance $R_T$ of the thermistor is calculated using the equation:

Use your data in Table 2.1 to calculate $R_T$ at room temperature $\theta_R$ and $R_T$ at the temperature of the hot water $\theta_H$.

$R_T$ at room temperature $\theta_R$ = ______ $\Omega$
$R_T$ at temperature of the hot water $\theta_H$ = ______ $\Omega$

Calculate $\alpha$, the average change in the resistance per degree Celsius for the thermistor as its temperature rises from room temperature $\theta_R$ to the temperature of the hot water $\theta_H$.

Use the equation shown.

$\alpha$ = ______ $\Omega / ^\circ\text{C}$

On Fig. 2.1, draw a normal to the line XY at point M. Extend the normal 8 cm above and 8 cm below the line XY.

On Fig. 2.1, draw a line from point M to the left of the normal above line XY so that the angle between the drawn line and the normal is $40^\circ$.

Label the top left-hand end of the line as point L.

Place the block with one of its long sides on the line XY.

The top left-hand side of the block should be at point X.

Draw the outline of the block on Fig. 2.1.

Do not remove the transparent block.

Using the illuminated slit, shine a narrow ray of light along the line LM.

Mark with small crosses (x) two points on the ray that emerges from the block.

Choose the position of the points so that the ray leaving the block can be drawn accurately.

Remove the glass block.

Join the marked crosses and extend the line to meet the lower end of the outline of the block.

Label the point where the line meets the block outline as point P.

Draw a straight line to join the points M and P.

The angle of refraction $r$ is the angle between the line MP and the normal drawn in (a)(i).

Measure and record angle $r$.

$r$ = ______ $^\circ$

The refractive index $n$ of the transparent block is given by the equation shown.

Calculate $n$ and give your answer to 2 significant figures.

$n$ = ______

Suggest how you could change the experiment to make sure that your value of $n$ is accurate.

Draw a diagram of the circuit arrangement using the correct symbols for the components in the circuit.

Choose from the symbols shown in Fig. 1.1.

You do not need to label points P, Q and S on your diagram.

Connect the voltmeter across the LDR between points P and Q.

Close the switch.

Record $V_{PQ}$, the voltmeter reading across P and Q.

This is $V_{PQ}$ under normal lighting conditions.

$V_{PQ}$ = ______ $\text{V}$

Open the switch.

Disconnect the voltmeter from points P and Q.

Reconnect the voltmeter across the 560 $\Omega$ resistor between points Q and S.

Close the switch.

Record $V_{QS}$, the voltmeter reading across Q and S.

$V_{QS}$ = ______ $\text{V}$

Open the switch.

The current $I$ in the circuit is calculated using the equation:

where $R = 560\ \Omega$.

Use your reading in (b)(ii) to calculate the current $I$.

$I$ = ______ $\text{A}$

Calculate the resistance $R_{\text{LDR}}$ of the LDR under normal lighting conditions using the equation shown.

$R_{\text{LDR}}$ = ______ $\Omega$

Disconnect the voltmeter from points Q and S.

Reconnect the voltmeter across the LDR between points P and Q.

Place the piece of card on top of the LDR.

Close the switch.

Record a new value of $V_{PQ}$ for the LDR in the dark.

$V_{PQ}$ = ______ $\text{V}$

Open the switch.

Compare your reading for $V_{PQ}$ with the LDR under normal lighting conditions in (b)(i) with $V_{PQ}$ with the LDR covered by card in (e).

Suggest what causes the change in the voltmeter readings as the intensity of the light reaching the LDR decreases.

Close the switch.

Hold the card horizontally about 50 cm above the LDR.

Slowly move the card towards the LDR until it rests on top of the LDR.

Observe the reading on the voltmeter as you move the card.

Open the switch.

Describe the changes you see to the voltmeter reading as the card is moved downwards.

Use the set squares to help you take readings on the metre rule of the positions of points A and B, as shown in Fig. 1.1. Give your readings to the nearest 0.1 $\text{cm}$.

position of point A = ______ $\text{cm}$
position of point B = ______ $\text{cm}$

The length $l$ is the distance between points A and B. The average diameter $d$ of one ball can be found using the equation:

Use your answers to (a)(i) to find length $l$ and diameter $d$. Give your answers to the nearest 0.1 $\text{cm}$.

$l$ = ______ $\text{cm}$
$d$ = ______ $\text{cm}$

The average volume $V$ of one glass ball found using this method is given by the equation:

Calculate $V$.

$V$ = ______ $\text{cm}^3$

Record the volume $V_1$ of the water in the measuring cylinder.

$V_1$ = ______ $\text{cm}^3$

• Carefully add the six glass balls to the water in the measuring cylinder.

Record the new volume $V_2$ of the water and glass balls in the measuring cylinder.

$V_2$ = ______ $\text{cm}^3$

The volume $V_T$ of the six balls is given by the equation:

Calculate $V_T$.

$V_T$ = ______ $\text{cm}^3$

• Remove the glass balls from the measuring cylinder and dry them using the paper towel.

Calculate the average volume $V$ of one ball found using this method.

$V$ = ______ $\text{cm}^3$

Suggest whether method 1 or method 2 gives the more accurate value for the volume of the ball.

Explain your answer.

method giving more accurate value ______
explanation ______

The average mass of a glass ball can be found using a small beaker and a top-pan balance.

Find the average mass of one glass ball using the small beaker and the top-pan balance supplied.

Describe your method and record the readings you take.

method ______

readings

mass of one glass ball = ______ $\text{g}$

Measure the temperature $\theta$ of the water and immediately start the stop-watch. Record this temperature in the first row of Table 2.1.

Record in Table 2.1 the temperature $\theta$ of the water every 30 $\text{s}$ for 4 minutes.

Table 2.1

Empty the 250 $\text{cm}^3$ beaker when you have finished taking the temperature of the water in it.

Calculate the average cooling rate $C_1$ of the water for the first 90 $\text{s}$ of the experiment. Use your readings in Table 2.1 and the equation:

where $\theta_0$ is the temperature at 0 $\text{s}$, $\theta_{90}$ is the temperature at 90 $\text{s}$ and $t$ is the time of 90 $\text{s}$.

Give the unit for $C_1$.

$C_1$ = ______ unit ______

Calculate the average cooling rate $C_2$ of the water for the final 90 $\text{s}$ of the experiment. Use the equation:

where $\theta_{150}$ is the temperature of the water at 150 $\text{s}$, $\theta_{240}$ is the temperature of the water at 240 $\text{s}$ and $t$ is the time of 90 $\text{s}$.

$C_2$ = ______ unit ______

Compare your values of $C_1$ and $C_2$. Explain any difference in these values.

Measure the temperature $\theta$ of the hot water and immediately start the stop-watch.

Record, in Table 2.2, the temperature $\theta$ at times $t = 0\ \text{s}$, 30 $\text{s}$, 60 $\text{s}$, 90 $\text{s}$ and 120 $\text{s}$.

Table 2.2

Calculate the average cooling rate $C_3$ for the first 90 $\text{s}$ of the experiment.

Use your readings in Table 2.2 and the equation:

$C_3$ = ______ unit ______

Describe how $C_3$ differs from $C_1$. Explain your answer.

State one variable that you should keep constant to make a valid comparison of $C_1$ and $C_3$.