IB-1 Physics Electrostatics Practice Questions. e +4e A. B. C. D.

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1 1. A plastic rod is rubbed with a cloth. At the end of the process, the rod is found to be positively charged and the cloth is found to be uncharged. This involves the movement of A. positive charge from the cloth to the rod. B. positive charge from earth to the cloth. C. negative charge from the rod to earth. D. negative charge from earth to the cloth. 2. Two charges of e and +4e are fixed at the positions shown below. At which position along the line is the electric field due to these charges equal to zero? e +4e A. B. C. D. 3. The diagram below shows lines of electric equipotential. The change in potential on moving from one line to the next is always the same. At which point does the electric field strength have its greatest magnitude? OMIT B A C D 4. Which one of the following is a correct definition of electric potential difference between two points? A. The power to move a small positive charge between the two points. B. The work done to move a small positive charge between the two points. C. The power per unit charge to move a small positive charge between the two points. D. The work done per unit charge to move a small positive charge between the two points. 5. Electric field strength is defined as A. the force exerted on a test charge. B. the force per unit positive charge. C. the force per unit charge. D. the force per unit charge exerted on a positive test charge. 1

2 6. The diagram below shows two lines of equipotential in a region of a uniform electric field. Line has a potential of +50 V and line has a potential of +100V. The distance between and is 2.0 cm. +50 V +100 V 2.0 cm Which one of the following correctly gives the direction of the electric field and its strength? Direction Strength / V cm 1 A. 25 B. 100 C. 25 D Two isolated spheres and of unknown materials are touching one another as shown below. sphere, earthed sphere, negatively charged Sphere is negatively charged and sphere is earthed. The earth connection is removed from sphere and then the spheres are separated as shown below. sphere, positively charged sphere, negatively charged Sphere is found to be positively charged and sphere remains negatively charged. Which of the following describes the nature of the materials from which the spheres are made? Sphere Sphere A. Insulator Insulator B. Insulator Conductor C. Conductor Insulator D. Conductor Conductor 2

3 8. The diagram below shows the electric field lines in a region of space. A positively charged particle moves from P to Q. P Q Which of the following is correct? Change in potential energy of particle Change in potential between P and Q A. decreases zero B. decreases negative C. increases zero D. increases negative 9. The diagram below illustrates some equipotential lines between two charged parallel metal plates m 80 V 60 V 40 V 20 V The electric field strength between the plates is A. 6 N C 1. B. 8 N C 1. C. 600 N C 1. D. 800 N C A proton and an alpha particle are accelerated from rest from the positively charged plate to the negatively charged plate proton alpha particle mid-point At the mid-point between the plates, the proton has a kinetic energy EK. At this point, the alpha particle has a kinetic energy A. E K. B. E K. C. 2EK. D. 4EK. 2 3

4 11. The diagram below shows some equipotential lines in an electric field V +290 V +280 V +270 V +260 V +250 V The magnitude of the electric field strength at is E and at is E. Which one of the following correctly compares E and E and gives the correct direction of the electric field? Magnitude of field strengths Direction of field A. E E B. E E C. E E D. E E 12. Three equal point charges, and Z are fixed in the positions shown. Z q m m q 1 q 2 The distance between q1 and q2 and the distance between q2 and q3 is 1.0 m. The electric force between the charges at and is F. The electric force between the charges at and Z is F A.. 2 F B.. 2 C. F. D. 2F. 4

5 13. A proton of mass m and charge e is accelerated from rest through a potential difference V. The final speed of the proton is 2Ve m A.. 2Ve B.. m Ve C.. m Ve D.. m 14. Which of the following statements is not true? A. Electric charge is quantized. B. Electric charge is conserved. C. The force between two point charges is proportional to the sum of the charges. D. The force between two point charges is proportional to the inverse square of the separation of the charges. 15. Which of the following correctly describes the nature of electric potential and electric field strength? Potential Field strength A. Scalar Scalar B. Scalar Vector C. Vector Scalar D. Vector Vector 5

6 16. A positively charged rod is brought close to an earthed sphere S, as shown below. S The earth connection to the sphere is removed and then the charged rod is removed. The sphere S is found to be negatively charged. Which one of the following describes the material of S and the movement of charge between S and earth? Material of S Movement of charge A. conductor negative charge moves from earth to S B. insulator negative charge moves from earth to S C. conductor positive charge moves from S to earth D. insulator positive charge moves from S to earth 17. Two charges of magnitude +2Q and Q are situated as shown below. At which point is the electric field due to the two charges most likely to be zero? +2Q Q A. B. C. D. 6

7 18. The diagram below shows two long parallel plates that are oppositely charged. A positive test charge +q is placed along the dotted line. + q The charge +q is moved from to. Which one of the following best shows the variation with distance d from of the magnitude F of the force on +q? A. F B. F 0 0 d d C. F D. F 0 0 d d 19. and are two identical conducting spheres separated by a distance d. has a charge +6 μc and has a charge 2 μc. The electric force between them is + F (ie attractive). The spheres are touched together and are then returned to their original separation d. The force between them now is F F A. +F. B. F. C.. D

8 20. An electrically neutral conducting sphere is suspended vertically from an insulating thread. thread Q sphere A point charge of magnitude Q is brought near the sphere. The electric force between the point charge and the sphere A. depends on whether Q is positive or negative. B. is always zero. C. is always repulsive. D. is always attractive. 21. Four point charges of equal magnitude Q are placed at the corners of a square as shown below. The centre of the square is at the origin of the x-axis and the y-axis. +Q y Q x +Q Q At which position, or positions, is the electric potential due to the four point charges equal to zero? A. At the centre of the square only. B. Along the x-axis only. C. Along the y-axis only. D. Along the x-axis and the y-axis. 8

9 22. An isolated, uncharged metal conductor is brought close to a positively charged insulator. insulating handle conductor insulator The conductor is earthed (grounded) for a short time and then the insulator is removed. Which of the following best represents the charge distribution on the surface of the conductor as a result of these actions? A. B. C. D. 23. A charged particle P is accelerated between two charged metal plates and separated by a distance d. The particle starts from rest at plate. P. plate plate d The kinetic energy of P, when it reaches plate, is K. The magnitude of the charge on P is e. The magnitude of the electric field strength between the plates is de A.. K d B.. Ke K C.. ed Ke D.. d 24. The work done on a positive point charge of magnitude 3.0 nc as it is moved at constant speed from one point to another is 12 nj. The potential difference between the two points is A. 0.0 V. B V. C. 4.0 V. D. 36 V. 9

10 25. Two charged plastic balls are separated by a distance d in a vertical insulating tube, as shown. tube balls d The charge on each ball is doubled. Coulomb s law applies to the force between the balls and friction with the walls of the tube is negligible. What is now the separation of the balls? A. d 2 B. d C. 2d D. 4d 10