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Question: Breakdown field strength for air is roughly . If the electric field is greater than this value, the air becomes a conductor. (a) There is a limit to the amount of charge that you can put on a metal sphere in air. If you slightly exceed this limit, why would breakdown occur, and why would the breakdown occur very near the surface of the sphere, rather than somewhere else? (b) How much excess charge can you put on a metal sphere of radius without causing breakdown in the neighboring air, which would discharge the sphere? (c) How much excess charge can you put on a metal sphere of onlyradius? These results hint at the reason why a highly charged piece of metal tends to spark at places where the radius of curvature is small, or at places where there are sharp points.

Short Answer

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Answer

(a) Electric breakdown occurs as the magnitude of the electric field is above the limit of the electric breakdown for a charged object. If the distance amongst the charged object and the point inside the electric field is decreased to a high value, then the electric field鈥檚 magnitude will exceed the value of the breakdown limit of the electric field, so that electric breakdown occurs near the sphere鈥檚 surface.

(b) The excess charge that can be put on a metal sphere is for a metal sphere of radius.

(c) The excess charge that can be put on a metal sphere is for a metal sphere of radius.

Step by step solution

01

Identification of given data

The given data is listed below as:

  • The strength of the breakdown field of air is,E=3106N/C
  • The radius of the metal sphere in the first case is,R1=10cm=10cm1m100cm=0.1m .
  • The radius of the metal sphere in the second case is R2=1mm=1mm1m1000mm=0.001m.
02

Significance of the electric field

The electric field is referred to as a region that helps an electrically charged particle to exert force on another particle. The magnitude of the electric field is directly proportional to the charge induced and inversely proportional to the square of their distances.

03

(a) Determination of the reason for the breakdown 

Electric breakdown happens because of the reason that the electric field鈥檚 magnitude of an object that is electrically charged is mainly above the limit of the electrical breakdown of a particular insulator that mainly surrounds an object that is charged.

If the distance amongst the charged object and the point inside the electric field is decreased to a high value, then the electric field鈥檚 magnitude will exceed the value of the breakdown limit of the electric field. Hence, it is the reason the breakdown occurs near the surface of the sphere.

Thus, electric breakdown occurs as the magnitude of the electric field is above the limit of the electric breakdown for a charged object. If the distance amongst the charged object and the point inside the electric field is decreased to a high value, then the electric field鈥檚 magnitude will exceed the value of the breakdown limit of the electric field, so that electric breakdown occurs near the sphere鈥檚 surface.

04

(b) Determination of the excess charge for a metal sphere of radius 

The equation of the magnitude of the electric field for a metal sphere is expressed as:

E=kqR12q=ER12k

Here, is the magnitude of the electric field that is the strength of breakdown field of air, is the electric constant with the value , is the excess charge and is the radius of the metal sphere in the first case.

Substitute the values in the above equation.

q=3106N/C0.1m29109Nm2/C2=3106N/C0.01m29109Nm2/C2=30000Nm2/C9109Nm2/C2=3.3310-6C

Thus, the excess charge that can be put on a metal sphere is for a metal sphere of radius.

05

(c) Determination of the excess charge for a metal sphere of radius

The equation of the magnitude of the electric field for a metal sphere is expressed as:

E=kqR22q=ER22k

Here, is the magnitude of the electric field that is the strength of breakdown field of air, is the electric constant, is the excess charge and is the radius of the metal sphere in the second case.

Substitute the values in the above equation.

q=3106N/C0.001m29109Nm2/C2=3106N/C110-6m29109Nm2/C2=3Nm2/C9109Nm2/C2=3.3310-10C

Thus, the excess charge that can be put on a metal sphere is for a metal sphere of radius.

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Most popular questions from this chapter

You stand at location A, a distance d from the origin, and hold a small charged ball. You find that the electric force on the ball is 0.08 N. You move to location B, a distance 2d from the origin, and find the electric force on the ball to be 0.04 N. What object located at the origin might be the source of the field? (1) A point charge, (2) A dipole, (3) A uniformly charged rod, (4) A uniformly charged ring, (5) A uniformly charged disk, (6) A capacitor, (7) A uniformly charged hollow sphere, (8) None of the above If the force at B were 0.0799 N, what would be your answer? If the force at B were 0.01 N, what would be your answer? If the force at B were 0.02 N, what would be your answer?

Question: A hollow ball of radius , made of very thin glass, is rubbed all over with a silk cloth and acquires a negative charge of that is uniformly distributed all over its surface. Location A in Figure 15.64 is inside the sphere, from the surface. Location B in Figure 15.64 is outside the sphere, from the surface. There are no other charged objects nearby.


Which of the following statements about , the magnitude of the electric field due to the ball, are correct? Select all that apply. (a) At location A, is . (b) All of the charges on the surface of the sphere contribute to at location A. (c) A hydrogen atom at location A would polarize because it is close to the negative charges on the surface of the sphere. What is at location B?

Two rings of radius5Cm are24 apart and concentric with a common horizontal x axis. The ring on the left carries a uniformly distributed charge of+31nC , and the ring on the right carries a uniformly distributed charge of-31nC. (a) What are the magnitude and direction of the electric field on the x axis, halfway between the two rings? (b) If a charge of-9nC were placed midway between the rings, what would be the force exerted on this charge by the rings?

A strip of invisible tape 0.12 mlong by 0.013 mwide is charged uniformly with a total net charge of 3nC(nano =110-9) and is suspended horizontally, so it lies along the xaxis, with its center at the origin, as shown in Figure 15.55. Calculate the approximate electric field at location<0,0.03,0>m(location A) due to the strip of tape. Do this by dividing the strip into three equal sections, as shown in Figure 15.55, and approximating each section as a point charge.

(a) What is the approximate electric field at Adue to piece 1? (b) What is the approximate electric field at Adue to piece 2? (c) What is the approximate electric field at Adue to piece 3? (d) What is the approximate net electric field at A? (e) What could you do to improve the accuracy of your calculation?

A student said, 鈥淭he electric field inside a uniformly charged sphere is always zero.鈥 Describe a situation where this is not true.

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