5. A positive point charge Q is located a distance x to the left of a negative p

Question

5. A positive point charge Q is located a distance x to the left of a negative point charge -2Q, with twice the magnitude, as shown in the image. Point P is located a distance x to the left of the positive charge What is the direction of the electric field at point P? -2Q a) Left c) The ficld is zero b) Right d) Not enough information 6. A proton is moving with constant velocity to the right (in the positive x direction) when it enters a region with an electric field directed to the right (in the positive x direction). Which of the ollowing accurately describes the motion of the proton in the region with the electric field? The proton will begin to curve upwards (in the positive y direction) The proton will begin to curve downwards (in the negative y direction) The proton will begin to speed up The proton will begin to slow down The proton will continue on unchanged a) b) c) d) e) 7. Rank the four situations shown to the right based on the magnitude of the electric field at the origin. In each case, an amount of charge as shown is spread evenly around the edge of some fraction of a circle 30 40 4 a) 1>2>3>4 b) 4>3>2>1 c) 3>2>1>4 A positive sodium ion (Na*) is fired into a region of electric field. The electric field is directed upwards, and the initial velocity is to the right, as indicated in the diagram. The path taken by the ion is best represented by which curve? 8. a) W b) X c) Y

Explanation / Answer

5)

Electric field at P due to -2Q:

E1 = k*(2Q)/(2x)^2 = kQ^2/2x^2 directed to the right

Similarly field at P due to Q:

E2 = k*Q/x^2 directed towards left

As E2 is greater than E1 , so net electric field will be directed towards E2.

So, answer is a) Left

6)

As the electric field is directed towards the directed towards the initial direction of motion, this force is in same direction as initial direction of motion. So, it will speed up.(option C)

7)

The electric fields due to the charge on the 1st quadrant and 3rd quadrant are equal and opposite (due to symmetry). So, the net electric field will be due to the charge on 2nd quadrant.

So, electric field due to arrangements 1 and 3 are same.

For arrangement 2, the electric field due to charge on 1st quadrant will be directed towards 45 deg south-west.

So, the component of this electric field along y-axis = E*cos(45) = E/sqrt(2)

Now, due to symmetry, the horizontal component of electric field due to the charge in the 2nd quadrant will cancel out the horizontal component of the electric field due to charge in 1st quadrant. And the vertical components will add up.

So, net field will be = 2*E*cos(45) = sqrt(2)*E

So, it's magnitude is greater than that of the arrangement in 1 or 3.

Now , due to symmetry, the net field in arrangement 4 will be 0.

So, the ranking is as follows:

2 > 1=3 > 4. Options e is correct.

8)

As the electric field is directed upwards , so the electric force on the Na+ ion is directed upwards. So, it will curve upwards .

So, answer is option C) Y

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