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TEST SERIES (PHYSICS FST)

266249 If the ratio of diameters, lengths and Young's modulus of steel and copper wires shown in the figure are $a, b$ and $c$ respectively, then the corresponding ratio of increase in their lengths would be:

\frac{2 a c}{b^{2}}

\frac{3 b}{2 a^{2} c}

\frac{3 c}{2 a b^{2}}

\frac{2 a^{2} c}{b}

Explanation:

b
$\begin{aligned} Δ L = \frac{F L}{A Y} = \frac{F L}{π D^{2} Y} \\ {\frac{Δ L_{s}}{Δ L_{c}} = \frac{F_{s}}{F_{c}} {(\frac{D_{c}}{D_{s}})}^{2})}_{c}^{Y_{s}} \times \frac{L_{s}}{L_{c}} \\ \frac{3}{2} {(\frac{1}{a})}^{2} (\frac{1}{c}) \times b = \frac{3 b}{2 a^{2} c} \end{aligned}$

**NCERT-XI-II-170

TEST SERIES (PHYSICS FST)

266250 Which one of the following is the property of a monochromatic, plane electromagnetic wave in free space:

1 Electric and magnetic fields have a phase difference of

π / 2

2 They travel with a speed equal to

\frac{1}{\sqrt{H_{0} ε_{0}}}

3 The direction of propagation is in the direction of

\vec{B} \times \vec{E}

E / B = 1

Explanation:

b
They travel with a speed equal to $\frac{1}{\sqrt{μ_{0} ε_{0}}}$

**NCERT-XII-I-207**

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TEST SERIES (PHYSICS FST)

\frac{2 a c}{b^{2}}

\frac{3 b}{2 a^{2} c}

\frac{3 c}{2 a b^{2}}

\frac{2 a^{2} c}{b}

Explanation:

**NCERT-XI-II-170

TEST SERIES (PHYSICS FST)

266250 Which one of the following is the property of a monochromatic, plane electromagnetic wave in free space:

1 Electric and magnetic fields have a phase difference of

π / 2

2 They travel with a speed equal to

\frac{1}{\sqrt{H_{0} ε_{0}}}

3 The direction of propagation is in the direction of

\vec{B} \times \vec{E}

E / B = 1

Explanation:

b
They travel with a speed equal to $\frac{1}{\sqrt{μ_{0} ε_{0}}}$

**NCERT-XII-I-207**

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