Consider a hydrogen atom with its electron in the $n$th orbit. An electromagnetic radiation of wavelength 90 nm is used to ionize the atom. If the kinetic energy of the ejected electron is 10.4 eV , then the value of $n$ is ( $h c=1242 \mathrm{eV} \mathrm{nm}$ )
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A water film is made between two straight parallel wires of length 10 cm each and at a distance of 0.5 cm from each other. If the distance between the wires is increased by 1 mm , then work done (in ergs) is [Given, surface tension of water $=72$ dynes $/ \mathrm{cm}$ ]
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The acceleration versus time graph of a particle moving along a straight line is shown in the figure. Draw the respective velocity time graph. (Assuming at $t=0, v=0$ )





In given lens combination, each lens is of focal length 10 cm .

Correct ray diagram for this combination is




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