unit4A-LEVEL A2 物理复习资料

Unit4 Physics on the Move

Section2 electric and magnetic field

1.electrostatics

(1)Electric field

(2)E=F/Q unit

(3)Electric field line(radial)

(4)F=KQ1Q2/r2

(5)E=kQ/r2

(201306r-4) Two protons, separated by a distance x, experience a repulsive force F.

If the separation is reduced to x/3 the force between the protons will be

A F/9

B F/3

C 3F

D 9F

(201206-4) A unit of electric field strength is

A . J C–2

B . N m2C–2 C. N m C–1 D . N C–1

(201206-11)The positively charged particles in the solar wind are accelerating away from the Sun. Some scientists have therefore concluded that the Sun is positively charged.

(a)Explain this conclusion.

(b) The circle below represents the Sun.

Complete the diagram to show the electric field produced by a positively-charged Sun.

（201001-11）The diagram represents a proton

(a) Draw lines to represent its electric field.

(b) Calculate the electrostatic force on the electron in a hydrogen atom.

Average distance between proton and electron = 5.4 x 10–11 m

(201301-14) Two identical table tennis balls, M and N, are attached to non-conducting threads and suspended from a point P. The balls are each given the same positive charge and they hang as shown in the diagram. The mass of each ball is 2.7 g. (a) Draw a free-body force diagram for ball M, label your diagram with the names of

the forces.

(b) (i) Show that the tension in one of the threads is about 3 ×10–2N. (ii) Show that the electrostatic force between the balls is about 2 × 10–2 N

(iii) Calculate the charge on each ball.

(c) State and explain what would have happened if the charge given to ball M was greater than the charge given to ball N.

(201106-16) (a) Sketch the electric field surrounding the gold nucleus drawn below.

(b) The spreadsheet shown approximately models the behaviour of an alpha particle

as it approaches a gold nucleus.

The proton number of gold is 79. mass of alpha particle=6.64×10–27kg

(i)Show how cell B3 is calculated.

(ii) Show how cell D5 is calculated.

(iii) Show how cell E6 is calculated

(iv) Suggest a value for the maximum radius of a gold nucleus based on the results from this spreadsheet.

*(c) Describe the conclusions Rutherford reached about the structure of gold atoms as

a result of the alpha particle scattering experiments.

2.capacitors

(1) structure

(2) Uniform electric field

(3) E=V/d C=Q/V

(4) W=1/2QV graph W=1/2CV2

（201306-3）Two parallel, conducting plates are connected to a battery. One plate is connected to the positive terminal and the other plate to the negative terminal. The plate separation d is gradually increased while the plates stay connected to the battery. Select the graph that shows how the electric field strength E between the plates varies with separation d.