![Electric fields, Electric field pattern, worked examples (A-level physics) Electric fields, Electric field pattern, worked examples (A-level physics)](https://digitalteachers.co.ug/wp-content/uploads/2021/10/Bbosa3-1973x2048-1.jpg)
Electric fields, Electric field pattern, worked examples (A-level physics)
Electric field
Al electric field is a region around an electric charge where an electric force is experienced. This can be mapped out by electrostatic lines of force.
A line of force is a line such that the tangent to it at any point is in the direction of the force on a small positive charge at that point. Arrows are drawn the direction and these point from positive towards or inwards to the negative charge. A collection of lines of force is called an electric flux.
Electric field pattern
- Two equal oppositely charged parallel plates
Definition
- A neutral point in an electric field is a point where the resultant electric field field intensity is zero.
The force exerted on the charged body in an electric field depends on the charge on the body and the intensity or strength of the field.
- Electric field intensity or strength is defined as the force exerted on a positive charge of 1 coulomb placed at a point in electric field
Therefore, electric field intensity, E is a vector quantity
The S.I. unit of E is NC-1
Consider the diagram below
Placing a small charge Q0 at point P, in an electric field, the force at P due to Q is given by
Note E is directed away from a positive charge and directed towards the negative charge.
Example 1
Find the electric field intensity at P
Solution
Solution
Example 2
Three point charges of +6.4μC, -6.4μC and +3.2μC are arranged in line at points A, B, and C respectively as shown in diagram above. Find the electric field intensity at P.
Solution
Hence the electric field at P is 1.472 x 105 NC-1 to the right
Example 3
Two point Charges P and S of -17.6μC and -9.0μC respectively are placed in a vacuum at a distance of 21cm apart. When a 3rd charge R is placed midway between P and S as shown in figure above, then, the net force at S is zero
(i) Determine the charge on R
(ii) Calculate the electric potential at position R.
(iii) Sketch the electric field lines corresponding to charge distribution
Solution
(ii) Electric field potential, at a distance r fro charge D is given by
Example 4
Calculate the electric field intensity midway between Q1 and Q2
Solution
Example 5
Charges Q1 and Q2 of -5μC and +2.0μC respectively are placed at two opposite corners of a rectangle of sides 5.0cm and 10.0cm as shown below
Calculate the electric field at A
Solution
Hence the electric filed intensity at A is 8.49 x 106 NC-1 at 580 to the horizontal
Example 6
Two point charges A and B of +10μC and +0.05μC are separated by a distance of 8cm along the horizontal as shown above. Find the electric field intensity at P.
Hence the electric field intensity at A is 3.55 x 105NC-1 at 660 to the horizontal
Example 7
Find the electric field intensity at P.
Solution
Hence the electric field intensity at P is 1.98 x 102 NC-1 at 450 to horizontal
Example 8
Two point charges are separated by 10cm in air as shown
Solution
Hence the electric field intensity at P is 4.5 x 105 NC-1 at 00 to the horizontal
Example 9
Two points +3.8μC and -5.2μC are place in air at points A and B as shown. Determine the electric field intensity at C
Solution
Hence the electric field intensity at C is 1.89 x 107NC-1 acting at 29.70 to horizontal.
Example 10
Three charges of -3 x 10-9C, +4 x 10-9C and +3 x 10-9C are placed at vertices A, B, C respectively of a rectangle ABCD of side 3cm x 4cm as shown. Calculate the resultant electric field intensity at D
Solution
Hence electric field intensity at D = 3.09 x 105NC-1 at 890 to horizontal
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