Question (1 Viewer)

Kaido · Feb 21, 2015

For Q5 of the below attachment, how would you know whether to start on +I or -I for the graph

Kaido · Feb 21, 2015

Another Q:
What is the difference between a voltage vs time graph and a Current vs time graph? Assume initial position to be parallel to the field and an AC gen.

InteGrand · Feb 21, 2015

Kaido said:
Another Q:
What is the difference between a voltage vs time graph and a Current vs time graph? Assume initial position to be parallel to the field and an AC gen.

Rate of change of the radius r is $\frac{\mathrm{dr} }{\mathrm{d} t}=-\frac{0.2-0.1}{0.2}=-\frac{1}{2} \text{ m/s}$ .

$\therefore r(t)=0.2-\frac{1}{2}t,$ $0\leq t\leq0.2$ (r in metres)

So the area of the ring as a function of time is $A(t)=\pi r^2 (t)=\pi \left (0.2-\frac{1}{2}t\right ) ^2$

$\therefore \Phi (t) = BA=2\pi \left (0.2-\frac{1}{2}t\right ) ^2$ (as magnetic field is a constant 2 T; units of the flux is T m²)

$\therefore \varepsilon(t) =-\frac{\mathrm{d\Phi} }{\mathrm{d} t}$ (Lenz's Law)

$\Rightarrow \varepsilon(t) =2\pi\left ( 0.2 - \frac{1}{2}t \right )=\frac{2\pi}{5}-\pi t$ . So you sketch this straight line for t from 0 to 0.2 s. (Units of the EMF is V (volts)). After 0.2 s, since the radius won't be changing then, the EMF will be 0.

InteGrand · Feb 21, 2015

Oops, was meant to reply to your first post.

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