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The current I in an inductance is varying with time according to the plot shown in the figure: it rises linearly from zero to its peak over the first half of the interval, then falls linearly back to zero over the second half. Which one of the following is the correct variation of voltage with time in the coil?

Asked in NEET 2012 · Behaviour of R, L and C separately

Figure: Behaviour of R, L and C separately
Answer: (4) a positive constant while the current rises, then a negative constant of the same size while it falls

Step-by-step solution

For an inductor V=L(dI)/(dt), so the voltage follows the slope of the current graph,

not its value.

On the rising half the slope is a positive constant, so the voltage holds one constant value.

At the peak the slope changes sign abruptly.

On the falling half the slope is a negative constant of the same size, so the voltage holds the

opposite constant value.

A triangular current therefore gives a square voltage waveform, switching between two levels with

no zero section in between - the current is never steady, so the voltage is never zero.

Why the other options are wrong

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