There are three voltmeters of the same range but of resistances $10000\,\Omega $, $8000\,\Omega $ and $4000\,\Omega $ respectively. The best voltmeter among these is the one whose resistance is ................ $\Omega $
Medium
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(a) Resistance of voltmeter should be high.
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A beam of protons with speed $4 \times 10^{5}\, ms ^{-1}$ enters a uniform magnetic field of $0.3\, T$ at an angle of $60^{\circ}$ to the magnetic field. The pitch of the resulting helical path of protons is close to....$cm$
(Mass of the proton $=1.67 \times 10^{-27}\, kg$, charge of the proton $=1.69 \times 10^{-19}\,C$)
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