The resistances of a wire at temperatures $t\,^oC$ and $0\,^oC$ are related by
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When a piece of aluminium wire of finite length is drawn through a series of dies to reduce its diameter to half its original value, its resistance will become ........ times
A wire of resistance $R$ and radius $r$ is stretched till its radius became $r / 2$. If new resistance of the stretched wire is $x R$, then value of $x$ is $\qquad$
Eels are able to generate current with biological cells called electroplaques. The electroplaques in an eel are arranged in $100$ rows, each row stretching horizontally along the body of the fish containing $5000$ electroplaques. The arrangement is suggestively shown below. Each electroplaques has an emf of $0.15\, V$ and internal resistance of $0.25 \,\Omega$ The water surrounding the eel completes a circuit between the head and its tail. If the water surrounding it has a resistance of $500 \,\Omega$, the current an eel can produce in water is about .............. $A$
Three unequal resistors in parallel are equivalent to a resistance $1\, ohm$. If two of them are in the ratio $1 : 2$ and if no resistance value is fractional, the largest of the three resistances in $ohms$ is
The number density of free electrons in copper is nearly $8 \times 10^{28}\,m ^{-3} . A$ copper wire has its area of cross section $=2 \times 10^{-6}\,m ^2$ and is carrying a current of $3.2\,A$. The drift speed of the electrons is $.....\times 10^{-6}\,ms ^{-1}$.