Which of the following wiring diagrams could be used to experimentally determine $R$ using Ohm's law? Assume an ideal voltmeter and an ideal ammeter.

If the direction cosines of two lines are such that $l+m+n=0$ and $l^2+m^2-n^2=0$,then the angle between them is:

If $\int \frac{e^x-1}{e^x+1} d x=f(x)+c$,then $f(x)$ is equal to

Which of the following orders is correct for the heat of hydrogenation of these compounds?

If $\alpha, \beta, \gamma$ are the roots of $x^3+4x+1=0$,then the equation whose roots are $\frac{\alpha^2}{\beta+\gamma}, \frac{\beta^2}{\gamma+\alpha}, \frac{\gamma^2}{\alpha+\beta}$ is

Charge $q$ is uniformly distributed over a thin half ring of radius $R$. The electric field at the centre of the ring is