physics question

[匿名]

2009-05-20 8:56 pm

Q 1 A charged conductor is brought near an uncharged insulator. Which one of the following statements is true?

A. Both objects will repel each other.

B. The objects will attract each other only if the conductor has a positive charge.

C. Both objects will attract each other.

D. Neither object exerts an electrical force on the other.

E. The objects will repel each other only if the conductor has a negative charge.

Q 2 A –4.0-µC charge is located 0.30 m to the left of a +6.0-µC charge. What is the magnitude and direction of the electrostatic force on the positive charge?

A. 4.8 N, to the left

B. 4.8 N, to the right

C. 2.4 N, to the left

D. 7.2 N, to the right

E. 2.4 N, to the right

Q 3 A completely ionized beryllium atom (net charge = +4e) is accelerated through a potential difference of 6.0 V. What is the increase in kinetic energy of the atom?

A. 6.0 eV

B. 4.0 eV

C. zero eV

D. 24 eV

E. 0.67 eV

Q 4 If the work required to move a +0.35 C charge from point A to point B is +125 J, what is the potential difference between the two points?

A. 88 V

B. 44 V

C. zero volts

D. 180 V

E. 360 V

please give detail solution or explain

thanks a lot

回答 (1)

Prof. Physics

2009-05-21 2:18 am

✔ 最佳答案

1. The answer is C.

When the charged object is brought near the neutral object, the face of the neutral object near the charged one would induce an opposite charge towards it, with the same charges being repelled. So, they would attract each other.

2. The answer is C.

The electrostatics force between them is attractive, so the force acting on the positive charge is towards left.

Force = 1/4piE0 Qq/r2

= 1/4pi(8.85 X 10-12) (-4.0 X 10-6)(6.0 X 10-6)/0.302

= -2.4 N

3. The answer is D.

By the law of conservation of energy

Loss of electrical potential energy = Gain of K.E.

Gain in K.E. = eV = 4(6.0) = 24 eV

4. The answer is E.

By U = qV

125 = 0.35V

Potential difference, V = 360 V

參考: Physics king

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