Physics

Contributor-Level 10

$λ_{electron} = \frac{h}{\sqrt[]{2 m E}} \frac{λ_{electron}}{λ_{photon}} = \frac{1}{c} \sqrt[]{\frac{E}{2 m}}$

$λ_{photon} = \frac{h c}{E}$

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5 months ago

The rms value of conduction current in a parallel plate capacitor is 6.9 $μ A$ . The capacity of this capacitor, if it is connected to 203 V ac supply with an angular frequency of 600 rad/s, will be:

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Contributor-Level 10

Current in capacitor l = $\frac{V}{X_{C}}$ $\frac{}{_{}}$

I = v * $(ω c)$

$C = \frac{1}{v ω} = \frac{6.9 * 1 0^{- 6}}{230 * 600} = 50 p F$

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5 months ago

A small square loop of wire of side $l$ is placed inside a large square loop of wire. L(L >> $l$ ). Both loops are coplanar and their centres coincide at point O as shown in figure. The mutual inductance of the system is:

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Contributor-Level 10

Assuming current 'i' In outer loop magnetic field at centre

$= 4 * \frac{μ_{0}}{4 π} \frac{i}{L / 2} * [2 s i n 45 °)$

$= \frac{2 \sqrt[]{2} μ_{0} i}{π L}$

M = $\frac{F m α t h r o u g h i n n e r l o o p}{i}$ $\frac{}{}$

= $\frac{2 \sqrt[]{2} μ_{0} i l^{2}}{π L} = \frac{2 \sqrt[]{2} μ_{0} l^{2}}{π L}$ $\frac{_{}^{}}{} \frac{_{}^{}}{}$

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5 months ago

In a building there are 15 bulbs of $45 W, 15$ bulbs of $100 W, 15$ small fans of $10 W$ and 2 heaters of $1 k W$ . The voltage of electric main is $220 V$ . The minimum fuse capacity (rated value) of the building will be

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Contributor-Level 10

Total power is $(15 * 45) + (15 * 100) + (15 * 10) + (2 * 1000) = 4325 W$

So, current is $\frac{4325}{220} = 19.66 A$

Answer is $20 A m p$ .

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5 months ago

To increase the resonant frequency in series LCR circuit,

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Physics Physics Moving Charges and Magnetism

Contributor-Level 10

$f = \frac{1}{2 π \sqrt[]{L C}}$

$f α \frac{1}{\sqrt[]{C}}$

Another capacitor should be added in series with the first capacitor.

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5 months ago

A particle of mass $m$ and charge $q$ has an initial velocity $\vec{v} = v_{0} \hat{j}$ . If an electric field $\vec{E} = E_{0} \hat{i}$ and magnetic field $\vec{B} = B_{0} \hat{i}$ act on the particle, its speed will double after a time:

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Physics Physics Moving Charges and Magnetism

Contributor-Level 10

Since magnetic force cannot change the speed. So only electric field which is along -direction will change the speed along -direction only.

$v_{x} = \frac{E_{0} q}{m} t$ but $v_{y} = v_{0}$

$2 v_{0} = \sqrt[]{v_{x}^{2} + v_{y}^{2}}$

4 v_{0}^{2} = \frac{E_{o}^{2} q^{2} t^{2}}{m^{2}} + v_{0}^{2}

t = \frac{\sqrt[]{3} m v_{o}}{q E_{o}}

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5 months ago

Two charged particles, having same kinetic energy, are allowed to pass through a uniform magnetic field perpendicular to the direction of motion. It the ratio of radii of their circular paths is 6 : 5 and their respective masses ratio is 9 : 4. Then, the ratio of their charges will be:

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Contributor-Level 10

Radius of circular path R = $\sqrt[]{\frac{2 m k}{q B}}$ $\frac{}{}$

$q = \frac{\sqrt[]{2 m k}}{R B}$

$\frac{q_{1}}{q_{2}} = \sqrt[]{\frac{m_{1}}{m_{2}}} * \frac{R_{2}}{R_{1}} = \sqrt[]{\frac{9}{4}} * \frac{5}{6} = \frac{5}{4}$

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5 months ago

A condenser of $2 μ F$ capacitance is charged steadily from 0 to 5 C. Which of the following graph represents correctly the variation of potential difference (V) across it's plates with respect to the charge (Q) on the condenser?

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Contributor-Level 10

Q = CV

$V = \frac{Q}{C}$

Straight line with slope = $\frac{1}{C ?}$ $\frac{}{}$

$S l o p e = \frac{1}{C} = \frac{1}{2 * 1 0^{- 6}} = 5 * 1 0^{5}$

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5 months ago

An emf of $20 V$ is applied at time $t = 0$ to a circuit containing in series $10 m H$ inductor and $5 Ω$ resistor. The ratio of the currents at time $t = \infty$ and at $t = 40 s$ is close to: (take $e^{2} = 7.389)$

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Contributor-Level 10

$\begin{array}{r} i & = \frac{V}{r} (1 - e^{- R t / L}) \\ = 4 (1 - e^{- 500 t}) \end{array}$

At $t = \infty$

$i_{1} = 4 A$

at $t = 40 s$

$i_{2} = 4 (1 - e^{- 20000})$

= 4 [1 - \frac{1}{{(e^{2})}^{10000}}]

= 4 [1 - \frac{1}{(7.389)^{10000}}]

\frac{i_{1}}{i_{2}}

is slightly greater than 1 .

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New answer posted

5 months ago

Physics Oscillations

In figure (A), mass '2 m' is fixed on mass 'm' which is attached to two spring of spring constant k. In figure (B), mass 'm' is attached to two springs of spring constant 'k' and '2k'. If mass 'm' in (A) and in (B) are displaced by distance 'x' horizontally and then released, then time period T₁ and T₂ corresponding to (A) and (B) respectively follow the relation.

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