<< Chapter < Page Chapter >> Page >

During electrical storms if you are driving a car, it is best to stay inside the car as its metal body acts as a Faraday cage with zero electrical field inside. If in the vicinity of a lightning strike, its effect is felt on the outside of the car and the inside is unaffected, provided you remain totally inside. This is also true if an active (“hot”) electrical wire was broken (in a storm or an accident) and fell on your car.

A cone shaped positively charged conductor is shown where most of the positive charges are accumulated at the tip. The field lines represented by arrows emerge at right angles from the surface of the conductor in outward direction. The density of field lines is greater at the tip of the cone than at other surfaces.
A very pointed conductor has a large charge concentration at the point. The electric field is very strong at the point and can exert a force large enough to transfer charge on or off the conductor. Lightning rods are used to prevent the buildup of large excess charges on structures and, thus, are pointed.
In part a, a lightning rod is shown on the roof of a house. In part b, a person is touching the metal sphere of the Van De Graaff and his hair is standing up.
(a) A lightning rod is pointed to facilitate the transfer of charge. (credit: Romaine, Wikimedia Commons) (b) This Van de Graaff generator has a smooth surface with a large radius of curvature to prevent the transfer of charge and allow a large voltage to be generated. The mutual repulsion of like charges is evident in the person's hair while touching the metal sphere. (credit: Jon ‘ShakataGaNai' Davis/Wikimedia Commons).

Test prep for ap courses

A gold sphere with eight equally spaced black +'s around the outside of the sphere point to eight blue arrows pointing outward. Four of the arrows point directly up, right, down, and left of the sphere and four arrows are equally spaced between these other four arrows at 45 degree angles. The arrow between the left and top arrow is labeled A. The arrow between the top and right arrow is labeled B. The arrow between the right and down arrow is labeled C.
A sphere conductor.

An electric field due to a positively charged spherical conductor is shown above. Where will the electric field be weakest?

  1. Point A
  2. Point B
  3. Point C
  4. Same at all points


Got questions? Get instant answers now!

There is a gray long thin rectangle at the top of the figure with black pluses. The same size gray long thin rectangle is at the bottom of the figure with minuses below the positives. There are blue lines with an arrow in the middle connecting each + to each -. The two arrows on the left start at the same first + are curved toward the left and hit the first bottom -. The two lines on the right are curved toward the right and connect the last + and -. The six center arrows are vertical. Between line three and four near the + rectangle is an A. A B is between lines four and five near the – rectangle. C is halfway between the + and – rectangle between lines six and seven.
Electric field between two parallel metal plates.

The electric field created by two parallel metal plates is shown above. Where will the electric field be strongest?

  1. Point A
  2. Point B
  3. Point C
  4. Same at all points
Got questions? Get instant answers now!

Suppose that the electric field experienced due to a positively charged small spherical conductor at a certain distance is E . What will be the percentage change in electric field experienced at thrice the distance if the charge on the conductor is doubled?

decrease by 77.78%.

Got questions? Get instant answers now!

The diagram shows an eye, microscope and then a gray bar with five +'s at the top, 5 arrows pointing directly down to 5 –‘s in a gray bar. In the center of the bars between the + and – bars is a gold drop.
Millikan oil drop experiment.

The classic Millikan oil drop experiment setup is shown above. In this experiment oil drops are suspended in a vertical electric field against the gravitational force to measure their charge. If the mass of a negatively charged drop suspended in an electric field of 1.18×10 −4 N/C strength is 3.85×10 −21 g, find the number of excess electrons in the drop.

Got questions? Get instant answers now!

Section summary

  • A conductor allows free charges to move about within it.
  • The electrical forces around a conductor will cause free charges to move around inside the conductor until static equilibrium is reached.
  • Any excess charge will collect along the surface of a conductor.
  • Conductors with sharp corners or points will collect more charge at those points.
  • A lightning rod is a conductor with sharply pointed ends that collect excess charge on the building caused by an electrical storm and allow it to dissipate back into the air.
  • Electrical storms result when the electrical field of Earth's surface in certain locations becomes more strongly charged, due to changes in the insulating effect of the air.
  • A Faraday cage acts like a shield around an object, preventing electric charge from penetrating inside.

Questions & Answers

Propose a force standard different from the example of a stretched spring discussed in the text. Your standard must be capable of producing the same force repeatedly.
Giovani Reply
What is meant by dielectric charge?
It's Reply
what happens to the size of charge if the dielectric is changed?
Brhanu Reply
omega= omega not +alpha t derivation
Provakar Reply
u have to derivate it respected to time ...and as w is the angular velocity uu will relace it with "thita × time""
do to be peaceful with any body
Brhanu Reply
the angle subtended at the center of sphere of radius r in steradian is equal to 4 pi how?
Saeed Reply
if for diatonic gas Cv =5R/2 then gamma is equal to 7/5 how?
define variable velocity
Ali Reply
displacement in easy way.
Mubashir Reply
binding energy per nucleon
Poonam Reply
why God created humanity
Manuel Reply
Because HE needs someone to dominate the earth (Gen. 1:26)
why god made humenity
Is the object in a conductor or an insulator? Justify your answer. whats the answer to this question? pls need help figure is given above
Jun Reply
ok we can say body is electrically neutral ...conductor this quality is given to most metalls who have free electron in orbital d ...but human doesn't have ...so we re made from insulator or dielectric material ... furthermore, the menirals in our body like k, Fe , cu , zn
when we face electric shock these elements work as a conductor that's why we got this shock
how do i calculate the pressure on the base of a deposit if the deposit is moving with a linear aceleration
ximena Reply
why electromagnetic induction is not used in room heater ?
Gopi Reply
What is position?
Amoah Reply
What is law of gravition
sushil Reply
Practice Key Terms 6

Get the best College physics for ap... course in your pocket!

Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics for ap® courses' conversation and receive update notifications?