Relative to resonance in sound wave, write the equation to determine the wavelength of sound in: (i) a close tube; (ii) an open tube.

(e)

(i) For a close tube, the wavelength $\lambda$ at resonance for the $n$-th harmonic (where $n$ is an odd integer, $n=1, 3, 5, ...$) is given by:

$$\lambda = \frac{4L}{n}$$

where $L$ is the length of the tube.

(ii) For an open tube, the wavelength $\lambda$ at resonance for the $n$-th harmonic (where $n$ is an integer, $n=1, 2, 3, ...$) is given by:

$$\lambda = \frac{2L}{n}$$

where $L$ is the length of the tube.

(a)

(i) Two differences between a primary cell and a secondary cell:

• A primary cell is non-rechargeable, while a secondary cell is rechargeable.
• The chemical reactions in a primary cell are irreversible, whereas in a secondary cell, they are reversible.

(ii) Two characteristics of an electromotive force (EMF):

• EMF is the maximum potential difference across the terminals of a cell when no current is drawn from it (open circuit).
• EMF is the work done per unit charge by the source in moving the charge around the complete circuit.

(iii) Electrical symbols:
I. Inductor:

\boxed{\text{—}\begin{tikzpicture}[baseline=(current bounding box.center)]\draw (0,0) sin (0.2,0.2) cos (0.4,0) sin (0.6,-0.2) cos (0.8,0) sin (1,0.2) cos (1.2,0);\end{tikzpicture}\text{—}}

II. Rheostat (variable resistor):

\boxed{\text{—}\begin{tikzpicture}[baseline=(current bounding box.center)]\draw (0,0) -- (0.2,0) -- (0.3,0.2) -- (0.5,-0.2) -- (0.7,0.2) -- (0.9,-0.2) -- (1.0,0.2) -- (1.2,0) -- (1.4,0);\draw[->] (0.1,0.3) -- (1.1,-0.1);\end{tikzpicture}\text{—}}

III. Diodes:

$$$$