A)The electric field can be calculated if the potential is known at several loca

Question

A)The electric field can be calculated if the potential is known at several locations; Find the magnitude of the electric field at location P. For distances, use the meter scale on the picture; measure to an appropriate degree of accuracy.

B) Find the direction of the electric field at location W in Fig. 2. Note that the electric field is always perpendicular to the contour lines. Give the direction as an angle (in degrees, measured anticlockwise from the x-axis).

1.5. * o voltages in volts 3 3 2 1 0 FIGURE 2 + -2.5 volts +-1.5 vols 5.0 volts 6.0 volts 7.0 volts 18.0Molts -3 volts -2 volts 90 • RR PP 135. 5 meters 10 PROTRACTORX 0 LLLLLLLLLL (Use this scale for figure 2 only.) 18+ –0 225 THX 315 270

Explanation / Answer

(A) Electric field is given by

E = -dV/dX

Point P is equidistant from lines with potential 1.5 V and 2.5 V.

Hence, electric field is uniform between potential 1.5 V and 2.5 V.

Now, dV between 1.5 and 2.5 V line = 1.0 V

Distance dX between 1.5 V and 2.5 V as measured from the given scale is

dX = 1.75 m

Hence, electric field E = 1/1.75 = 0.5714 V/m

+ve sign shoes that direction of electric field is towards positive x direction.

(B) As the potential is max at central contour lines and min outside lines, direction of electric field is radially outwards.

As measured from the protactor, the angle made by electric field lines with positive x axis is 75o.

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