AQA A2 Physics P22 Electrical Fields Kerboodle Answers

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22.1 Field patterns AQA A2 Physics P22 Electrical Fields Kerboodle Answers: Page No. 361

1.Ans-a) An insulated metal can is given a positive charge by touching it with a positively charged rod. Metals have de-localised electrons which are able to move to the positively charged rod to cancel the charge on the rod. This leaves a fewer electrons back on the metal can and as a result it acquires a positive charge. bThe electrons are mobile and so when the negatively charged sphere is connected to the ground via a wire these mobile electrons will move to the ground and the sphere discharges. 2.Ans- a) i 75nA ii 1.9 x 10¹¹ 3Ans-a) Like charged repel. The earthed conductor has undergone polarization with negative and positive charged distributed evenly. The action of the negatively charged object repels the negative electrons of the free conductor. b The earth acts as a source of positive and negative charge. The charged object is brought into proximity with the conductor which is then earthed. The object’s negative charge will attract positive charges from the earth into the object. Once it is unearthed the positive charges cannot leave the conductor, so when the object is removed the positive charge remains.

22.2 Electric field strengthAQA A2 Physics P22 Electrical Fields Kerboodle Answers: Page No. 365

1.a) Calculate the magnitude of the force On if the electric field strength where 01 is placed is 3.5 104 Vm-l. 1.4 x 10^-3 N b )4.0×10^-4 vm^-1 2.a)i Describe the type of charge carried by X. negative ii Calculate the charge carried by the particle. 1.3 x 10⁷ c b.i 7.3 x 10^-3 N ii State the direction of the force on the particle when it is at Y. Towards the metal surface 3.a The voltage is adjusted to 4.5kV. Calculate: i the electric field strength between the plates, 9.0 x 10⁴ v m^-1 ii the electrostatic force on a droplet in the field that carries a charge Of 8.0 x IO- 7.2 x 10^-14 N b.80mm 4.Ans a 2.9 kV b i 5.6 x 10^-15N

22.3 Electric potential AQA A2 Physics P22 Electrical Fields Kerboodle Answers : Page No. 368

I.Ans.a) the potential energy of the electron at i -soy, -8.0 x 10^-18 J ii +450″, +7.2 x 10^-17 J b +8.0 x 10^-17 J 2 a) if F+3.OpC, -1.8 x 10^-3 J b +1.2 x 10^-3 J 3.a) i 250 V m^-1 ii the force on the droplet. 8.0 x 10-17 N (towards the negative plate) b -8.0 x 10^-19 J 4 a Electric potential, the amount of work needed to move a unit charge from a reference point to a specific point against an electric field. SI unit is joule per coulomb i.e Volts b i 3000 V m^-1

22.4 Coulomb’s law AQA A2 Physics P22 Electrical Fields Kerboodle Answers : Page No. 371

  1a  protonat a distance of 2.5* 10-9m, 3.7 x 10^-11 N b a nucleus of a nitrogen atom (charge +?e) at a distance Of 2.s 2.6 x 10^-10 N 2 a i the distance d between the two charges, 69 mm ii 3.6×10^-6 N b A charge of +4.0nC is added to each charge in part a. Calculate the force between 01 and when they are at separation d. 2.5 x 10^-5 N repulsion 3 a 6.1 nC, negative b The two charges are moved 2.5 mm further part. Calculate the force between them in this new position. 2.2x 10^-2 N 4 a) Calculate the magnitude, O, Of each charge, and State whether the charges attract or repel each other. 2.7 nC, attract b 6.2 x 10^-2 m, repel

22.5 Point charges AQA A2 Physics P22 Electrical Fields Kerboodle Answers : Page No. 374

1 a 5.3 x 10⁶ V m^-1 b 10mm 2 a i 3.7 x 10⁸ V m^-1 ii 5.6 x 10^-3 N towards Q₁ 3a Calculate the resultant electric field strength: i 4.5 x 10⁸ V m^-1 towards Q₂ ii 2.6 x 10⁸ V m^-1 away from Q₁ b i Explain whu there is a point along the line between the two charges at which the electri field strength is zero. ii. 11 mm from Q1, 9 mm from Q2 4 a -9.0 x 10⁶ V b i Show that the electric potential is zero at a point between the two charges which is 10 mm from and 20 mm from ii 2.0 x 10⁹ V m^-1 directly towards Q₂ Banner 2

Practice questions: Page No. 376-379

(a) (i) The electric field strength at a point is the force per unit charge…acting on a small positive test charge placed at the point. (ii) E is a vector quantity. (b) (i) (ii) (c (i)

• Two lines with arrows at P, one representing

E4 directed outwards away from the 4 nC charge and the other representing E8 directed inwards towards the 8 nC charge.

• E8 twice as long as E4.
• Arrowed line R, the correct resultant of the parallelogram, drawn through the common point of E8 and E4.

2 (a) (b) (i) (ii) 3 a (i) Electric potential is taken to be zero at infinity. A positive test charge would gain potential energy as it was moved away from the negative charge and towards infinity. (ii) Three radial straight lines drawn so that they all end on the charge at Q. Arrows marked on all of the lines, pointing inwards to Q. b (i) (ii) Calculate the electric field strength at B.  (4 marks) c (i) (ii)

• The electron loses potential energy as it moves away from Q.
• As it moves away its speed will increase.
• Its de Broglie wavelength will decrease…
• because its momentum will increase.

4

• (i)
• Diagram drawn to show:
• An arrow, horizontal to the right, representing vH (or 20 m s−1) and an arrow from the same point, vertically downwards, representing vV.
• An arrow from the same point, at 35° to the horizontal, along the diagonal of the parallelogram representing the resultant velocity v.

From the diagram it will be seen that (ii) (iii) (iv) (v) (b)   5

• (i)

(ii) (b)   (i) , (ii) 6 (a) Figure 6 shows a small charged metal sphere carrying a charge Q. The potential of the sphere is 8000 V. Copy Figure 6. (i) Draw On your diagram at least six lines to show the direction of the electric field in the region around the charged sphere. (ii) Draw on your diagram the equipotential lines for potentials of 4000V and 2000 v. (iii)     ε0 is the permittivity of free space. (b)     (i) . Nylon is used for the thread because it is a good insulator. (ii) (iii) (iv) (c) (i)   (ii) In practice the oscillations are damped. Sketch a graph showing how the amplitude of the oscillations changes with time for the damped oscillation. (5 marks) AOA. 2007   7

• (i)
• At B, field strength E = 21 N C–1 (or V m–1)

Line drawn on graph:

• Starts at (6.4, 84) and is a curve of decreasing gradient …
• passes through (12.8, 21) and does not meet or intersect r axis

(ii) The pd between A and B can be found from the graph by determining the area enclosed between the line and the r axis between r = 6.4 and 12.8 × 10³ km

• (i)

(ii) Banner 3

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