Electric Charge, Coulomb's Law, Field and Potential

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.The SI unit of electric charge is:

   • A.ampere
   • B.coulomb✓ Correct Answer
   • C.volt
   • D.farad

   Explanation: One coulomb is the charge carried by one ampere in one second.

2. Q2.Two like charges:

   • A.attract each other
   • B.repel each other✓ Correct Answer
   • C.do not interact
   • D.cancel each other

   Explanation: Unlike charges attract.

3. Q3.An electron carries a:

   • A.positive charge
   • B.no charge
   • C.negative charge✓ Correct Answer
   • D.variable charge

   Explanation: The proton carries an equal positive charge.

4. Q4.The electron was discovered by:

   • A.Ernest Rutherford
   • B.James Chadwick
   • C.Niels Bohr
   • D.J. J. Thomson✓ Correct Answer

   Explanation: Thomson identified it in cathode rays in 1897.

5. Q5.The SI unit of potential difference is:

   • A.ampere
   • B.ohm
   • C.volt✓ Correct Answer
   • D.coulomb

   Explanation: One volt is one joule per coulomb.

6. Q6.A gold-leaf electroscope is used to:

   • A.measure current
   • B.measure temperature
   • C.detect the presence of electric charge✓ Correct Answer
   • D.measure mass

   Explanation: The leaves diverge when charged.

7. Q7.Coulomb's law says the force between two point charges is:

   • A.proportional to the product of charges and inversely proportional to the square of the distance✓ Correct Answer
   • B.proportional to the distance
   • C.independent of the charges
   • D.proportional to the sum of charges

   Explanation: F = k q1 q2 / r².

8. Q8.The magnitude of the charge on an electron is about:

   • A.1.6 × 10^-19 C✓ Correct Answer
   • B.1.6 × 10^19 C
   • C.9.1 × 10^-31 C
   • D.6.67 × 10^-11 C

   Explanation: 9.1 × 10^-31 kg is its mass.

9. Q9.Electric field lines originate from:

   • A.positive charges✓ Correct Answer
   • B.negative charges
   • C.neutral bodies
   • D.the centre of the Earth

   Explanation: They end on negative charges and never cross.

10. Q10.The SI unit of electric field strength is:

    • A.newton per metre
    • B.coulomb per volt
    • C.newton per coulomb✓ Correct Answer
    • D.joule per second

    Explanation: It equals volt per metre.

11. Q11.The SI unit of capacitance is:

    • A.henry
    • B.weber
    • C.tesla
    • D.farad✓ Correct Answer

    Explanation: One farad is one coulomb per volt.

12. Q12.A lightning conductor protects buildings by:

    • A.absorbing the lightning
    • B.reflecting lightning
    • C.cooling the air
    • D.discharging the charge safely to the ground through a pointed metal rod✓ Correct Answer

    Explanation: The pointed end leaks charge and provides an easy path to earth.

13. Q13.Inside a charged conductor in electrostatic equilibrium the electric field is:

    • A.zero✓ Correct Answer
    • B.maximum
    • C.equal to the surface value
    • D.infinite

    Explanation: Charges move until the internal field cancels.

14. Q14.Potential difference between two points is the:

    • A.current per unit time
    • B.charge per unit area
    • C.force per unit mass
    • D.work done per unit charge in moving a charge between them✓ Correct Answer

    Explanation: V = W/q.

15. Q15.Which of the following is a good electrical insulator?

    • A.copper
    • B.rubber✓ Correct Answer
    • C.silver
    • D.aluminium

    Explanation: Rubber has almost no free electrons.

16. Q16.A glass rod rubbed with silk becomes:

    • A.negatively charged
    • B.positively charged✓ Correct Answer
    • C.uncharged
    • D.magnetised

    Explanation: Glass loses electrons to silk.

17. Q17.Millikan's oil-drop experiment determined the:

    • A.mass of a proton
    • B.speed of light
    • C.charge of an electron✓ Correct Answer
    • D.gravitational constant

    Explanation: It showed that charge is quantised.

18. Q18.Quantisation of charge means that any charge is:

    • A.an integral multiple of the electron charge✓ Correct Answer
    • B.any real number times e
    • C.always zero
    • D.always continuous

    Explanation: q = ne, where n is an integer.

19. Q19.When capacitors are connected in parallel, the equivalent capacitance is:

    • A.the reciprocal of the sum
    • B.the product of capacitances
    • C.the smallest of them
    • D.the sum of the individual capacitances✓ Correct Answer

    Explanation: C = C1 + C2 + ...

20. Q20.A Faraday cage shields its interior from:

    • A.gravity
    • B.external static electric fields✓ Correct Answer
    • C.sound
    • D.all magnetism

    Explanation: A conducting enclosure keeps the field inside it zero.