B is the answer...
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I am assuming you know the relation obtained between slit width, distance of screen from slits, distance of interference pattern obtained on the screen from the center and the wavelength of monochromatic light used in Young's Double Slit experiment.
λ =

λ ~ 1.97 ×10⁻⁷m
Mechanical advantage is the amount by which a machine multiplies input force. It is a measure of the force amplification using a tool or machine system.
A) Agreed.
<span>b) Value agreed but units should be W (watts). </span>
<span>c) Here's one method... </span>
<span>15 miles = 24140 m </span>
<span>1 gallon of gasoline contains 1.4×10⁸ J. </span>
<span>So moving a distance of 24140m requires gasoline containing 1.4×10⁸ J </span>
<span>Therefore moving a distance of 1m requires gasoline containing 1.4×10⁸/24140 = 5800 J </span>
<span>Overcoming rolling resitance for 1m requires (useful) work = force x distance = 1000x1 = 1000J </span>
<span>So 5800J (in the gasoline) provides 1000J (overcoming rolling resistance) of useful work for each metre moved. </span>
<span>Efficiency = useful work/total energy supplied </span>
<span>= 1000/5800 </span>
<span>= 0.17 (=17%) </span>
Answer:
<em>a) 0.72 V</em>
<em>b) 19.2 mA</em>
<em>c) 2.304 Watts</em>
Explanation:
A transformer is used to step-up or step-down voltage and current. It uses the principle of electromagnetic induction. When the primary coil is greater than the secondary coil, the it is a step-down transformer, and when the primary coil is less than the secondary coil, the it is a step-up transformer.
number of primary turns =
= 500 turns
input voltage =
= 120 V
number of secondary turns =
= 3 turns
output voltage =
= ?
using the equation for a transformer

substituting values, we have


= 360/500 =<em> 0.72 V</em>
<em></em>
b) by law of energy conservation,

where
= input current = ?
= output voltage = 3.2 A
= output voltage = 0.72 V
= input voltage = 120 V
substituting values, we have
120
= 3.2 x 0.72
120
= 2.304
= 2.304/120 = 0.0192 A
= <em>19.2 mA</em>
<em></em>
c) power input = 
==> 0.0192 x 120 = <em>2.304 Watts</em>