$(a)$ Write two points of difference between sound wave and light wave.
$(b)$ Write an expression relating wave velocity, wavelength and frequency if speed of sound in air is $340 \, m s^{-1}$.
Calculate:
$(i)$ Wavelength when frequency $= 256 \, Hz$.
$(ii)$ Frequency when wavelength $= 0.85 \, m$.

(A) Two differences are as follows:

Sound Waves	Light Waves
$1.$ Longitudinal waves.	$1.$ Transverse waves.
$2.$ Require a material medium to propagate.	$2.$ Do not require a material medium to propagate.

$(b)$ The expression relating wave velocity $(v)$, frequency $(f)$, and wavelength $(\lambda)$ is: $v = f \times \lambda$.
Given: Speed of sound $(v)$ $= 340 \, m s^{-1}$.
$(i)$ Given frequency $(f)$ $= 256 \, Hz$. Using the formula $\lambda = v / f$:
$\lambda = 340 / 256 = 1.328 \, m \approx 1.33 \, m$.
$(ii)$ Given wavelength $(\lambda)$ $= 0.85 \, m$. Using the formula $f = v / \lambda$:
$f = 340 / 0.85 = 400 \, Hz$.