No questions found
As a bar magnet is dropped through a coil, an e.m.f. is induced in the coil. The maximum e.m.f. $E$ is induced as the magnet leaves the coil with speed $v$.
It is suggested that $E$ is directly proportional to $v$.
Design a laboratory experiment to test the relationship between $E$ and $v$. You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to
(a) the procedure to be followed,
(b) the measurements to be taken,
(c) the control of variables,
(d) the analysis of the data,
(e) the safety precautions to be taken.
546
556
561
Different light-emitting diodes (LEDs) can emit electromagnetic radiation of different wavelengths. A student uses the circuit of Fig. 2.1 to investigate the minimum potential difference required to cause an LED to emit its characteristic wavelength.
For different LEDs emitting radiation of wavelength $\lambda$, the minimum potential difference $V$ is recorded.
It is suggested that $V$ and $\lambda$ are related by the equation
$$ \frac{hc}{\lambda} = B + eV $$
where $c$ is the speed of light in a vacuum, $e$ is the elementary charge, $h$ is the Planck constant and $B$ is a constant.
(a) A graph is plotted of $V$ on the y-axis against $1/\lambda$ on the x-axis. Determine expressions for the gradient and y-intercept in terms of $B$, $c$, $e$ and $h$. [1]
(b) Values of $\lambda$ and $V$ are given in Fig. 2.2.
Calculate and record values of $(1/\lambda)/10^6 \text{m}^{-1}$ in Fig. 2.2. [2]
(c) (i) Plot a graph of $V/V$ against $(1/\lambda)/10^6 \text{m}^{-1}$. Include error bars for $V$. [2]
(ii) Draw the straight line of best fit and a worst acceptable straight line on your graph. Both lines should be clearly labelled. [2]
(iii) Determine the gradient of the line of best fit. Include the uncertainty in your answer. [2]
(iv) Determine the y-intercept of the line of best fit. Include the uncertainty in your answer. [2]
(d) (i) Using your answer to (c)(iii), determine a value for $h$.
Data: $c = 3.0 \times 10^8 \text{ms}^{-1}$ and $e = 1.6 \times 10^{-19}$ C. [1]
(ii) Determine the percentage uncertainty in your value of $h$. [1]
(e) Using your answer to (c)(iv), determine a value for $B$. Include an appropriate unit and the absolute uncertainty in your answer. [2]
521
597
585
