11.AQA OCR Edexcel A Level Physics Electric Fields Answers

A Level Physics Electric Fields 1 (Answers) Total Marks:/30 AQA, Edexcel, OCR A Level Solution: The force experienced per unit positive charge at that point. Solution: Similarities: both have dependence on product of two charges/masses; both have inverse square law dependence on distance; point charges/masses produce radial fields. Differences: whilst gravitational fields are always attractive, electric fields can also be repulsive. 1. Total for Question 1: 13 (a) Define the electric field strength at a point in space. [1] [2] (b) State one similarity and one difference between the electric fields produced by charges and the gravitational fields produced by masses. (c) Which two of the following statements are true? i. The direction of an electric field is that in which a negative charge would move. ii. Electric field lines are always perpendicular to the surface of a conductor. iii. The spacing of electric field lines is directly proportional to the field’s strength. iv. The direction of an electric field is that in which a positive charge would move. [2] Solution: 2 and 4. Solution: All sketches below should adhere to the simple rules of field lines: perpendicular to conductors’ surfaces; arrows from + to -; uniformity indicated by equal spacing; greater strength represented by more closely spaced lines. Solution:Radial field with arrows pointing inwards. Lines should be straight. Solution: Uniform field in the middle region of the plates; towards the ends the field lines should bow out. (d) Sketch the electric fields produced by the following: i. A negative point charge. [1] ii. A positively charged sphere. [1] iii. Two parallel plates with opposite charges. [2] Solution: Radial field with arrows pointing outwards. Lines should be straight. iv. Two spheres with opposite charges. [2] Solution: Densely spaced lines where the surfaces are closest together; more widely spaced lines fanning out elsewhere. Lines from outside edges need not be joined up to h th v. A positively charged sphere and a negatively charged plate. [2] Solution: Strongest field where surface separations are smallest. 4 9 2. A metal sphere has a radius, r, of 1.0 m and a positive charge of 5.0 × 10 −7 C. Total for Question 2: 9 (a) Calculate the electric field strength at a distance, d, of 1.0 m from the surface of the sphere. [3] (b) Without repeating the full calculations you performed in the previous part, determine how the calculated field strength would change in the following circumstances. i. The charge doubles. [1] ii. r triples. [2] Solution: × 1 iii. d is five times larger. [3] Solution: × 1 Solution:×2 Solution: 1100 NC−1 Solution: 8.4 × 107 ms −1 Solution: 0.67 m 3. An electron is accelerated from rest by a uniform electric field. Given that the field strength is 1.2 × 105 NC −1, calculate the following: (a) The force experienced by the electron. Total for Question 3: 8 [2] (b) Its speed after 4 ns. [3] (c) Its displacement after 8 ns. [3] Solution: 1.9 × 10−14 N