DHS 15 Electric Fields (Notes & Tutorial)

Dunman High School (Senior High Physics) 9749 Physics (2025) Topic 13: Electric Fields Page 1 of 39 Guiding Questions  What is electric charge? How do charges interact?  What do field lines represent? Do field lines represent similar things for gravitational fields and electric fields? Content  Concept of an electric field  Force between point charges  Electric field of a point charge  Uniform electric fields  Electric potential Learning Outcomes Students should be able to: Concept of an electric field (a) show an understanding of the concept of an electric field as an example of a field of force and define electric field strength at a point as the electric force exerted per unit positive charge placed at that point (b) represent an electric field by means of field lines (c) recognise the analogy between certain qualitative and quantitative aspects of electric field and gravitational field Electric force between point charges (d) recall and use Coulomb's law in the form 2 1 2 4 oF Q Q r  for the electric force between two point charges in free space or air Electric field of a point charge (e) recall and use 24 oE Q r  for the electric field strength of a point charge in free space or air Uniform electric fields (f) calculate the electric field strength of the uniform field between charged parallel plates in terms of potential difference and separation (g) calculate the forces on charges in uniform electric fields (h) describe the effect of a uniform electric field on the motion of charged particles Electric potential (i) define the electric potential at a point as the work done per unit positive charge in bringing a small test charge from infinity to that point (j) state that the field strength of the electric field at a point is numerically equal to the potential gradient at that point. (k) use the equation 4 oV Q r  for the electric potential in the field of a point charge, in free space or air. 9749 H2 Physics Topic 13 Electric Fields Year 6 (2025) DUNMAN HIGH SCHOOL

Dunman High School (Senior High Physics) 9749 Physics (2025) Topic 13: Electric Fields Page 2 of 39 (c) recognise the analogy between certain qualitative and quantitative aspects of electric field and gravitational field. 1. Analogy between electric field and gravitational field field: electric gravitational force [discussed in detail in learning outcome (d)]  2 1 r  1 2 2e Q QF k r      [Coulomb’s law]  between two point charges Q1 and Q2  SI units: N  a vector  2 1 r  2'g MmF k r      [Newton’s law of gravitation]  between two point masses M and m  SI units: N  a vector force acts on: object with charge only object with mass only field strength [discussed in detail in learning outcome (e)] FE q (definition)  2 1 r  1 2 QE k r       due to a point charge Q1 [in a vacuum (free spac