(a) State an expression for the electric field strength E at a distance r from a point charge Q in a vacuum. State the name of any other symbol used. (b) Two point charges A and B are situated a distance 10.0 cm apart in a vacuum, as illustrated in Fig. 6.1. [Figure 6.1] A point P lies on the line joining the charges A and B. Point P is a distance x from A. The variation with distance x of the electric field strength E at point P is shown in Fig. 6.2. [Figure 6.2]

1. (a)State an expression for the electric field strength E at a distance r from a point charge Q in a vacuum. State the name of any other symbol used.[2]
2. (b)(i)State and explain whether the charges A and B: have the same, or opposite, signs[2]
3. (b)(ii)State and explain whether the charges A and B: have the same, or different, magnitudes.[2]
4. (c)An electron is situated at point P. Without calculation, state and explain the variation in the magnitude of the acceleration of the electron as it moves from the position where x = 3 cm to the position where x = 7 cm.[4]

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