$R _{ p }=800\,\Omega$
$\frac{(160)^{2}}{R_{S}}=80 \times 10^{3}$
$R _{ S }=0.32\,\Omega$
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Reason : Paraxial rays incident parallel to principal axis intersect at the focus after refraction from lens.

$A$. In a plane electromagnetic wave electric field and magnetic field must be perpendicular to each other and direction of propagation of wave should be along electric field or magnetic field.
$B.$ The energy in electromagnetic wave is divided equally between electric and magnetic fields.
$C.$ Both electric field and magnetic field are parallel to each other and perpendicular to the direction of propagation of wave.
$D.$ The electric field, magnetic field and direction of propagation of wave must be perpendicular to each other.
$E.$ The ratio of amplitude of magnetic field to the amplitude of electric field is equal to speed of light.
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