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Exam 17: Electric Energy and Potential

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Question 21

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How would you expect the dielectric constant of a material to depend on the dipole moment of the constituent molecules?

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The electric field of the plates tends t...

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Question 22

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The potential across a cell membrane of thickness 0.5 ìm increases by 75 mV from inside to outside. What is the surface charge density on the outside surface of the membrane?

A) 1.5 ìC/m²
B) -1.5 ìC/m²
C) 0.8 ìC/m²
D) -0.8 ìC/m²

E) A) and C)
F) A) and B)

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Question 23

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What property of a defibrillator contributes most to improving the survival probability of a cardiac patient?

Regarding Earth and a cloud layer 1000 m above Earth as the "plates" of a capacitor, calculate the capacitance if the cloud layer has an area of 1.0 km². If an electric field of 2.0 × 10⁶ V makes the air break down and conduct electricity (lightning), what is the maximum charge the cloud can hold?

The change in potential energy of a particle in an electric field is the negative of the work done by an external force on displacing the particle.

An electron is near a positive ion. The electron moves toward the ion. Which of these statements is an accurate description of the work done by the ion on the electron?

If you were required to build a capacitor that was both small and had a high capacitance, what factors would you need to consider in its design?

A charge of 1 ìC is spread uniformly around a ring of radius 10 cm. What is the potential at a point located 5 cm from the centre, along the axis of the ring?

Calculate the value of the electric field across a human nerve membrane. The value of potential difference is 70 mV, and the width of the membrane (the distance between positive and negative plates) is 6 nm.

A uniform electric field of magnitude 150 V/m is directed in the positive x-direction. A +12.0 ìC charge moves from the origin to the point (x, y) = (20.0 cm, 25.0 cm) . Through what potential difference does the charge move?

At which position between parallel oppositely charged plates is the electric energy of a negative point charge at maximum?

An initially uncharged parallel plate capacitor is charged by a battery. The battery is then disconnected. Which of these statements applies at that point?

A free electron and a proton are released from rest halfway between a pair of oppositely charged parallel plates. The proton, being the heavier particle, will reach the negative plate before the electron reaches the positive plate.

If a charged particle moves along a path for which its displacement at each point is perpendicular to the electric field at that point, then its potential energy remains constant on that path.

A parallel plate capacitor of capacitance C0 has plates of area A with separation b between them. When the capacitor is connected to a battery of voltage ÄV, it has a charge of magnitude Q on its plates. It is then disconnected from the battery and the space between the plates is filled with a material of dielectric constant ê = 3. After the dielectric material is added, what is the potential difference between the plates?

How much energy is stored in a 10 µF capacitor when ÄV = 25 V?

The plates of a charged capacitor attract each other due to the electric forces between them. Suppose the capacitor is disconnected from the battery used to charge it, so the amount of charge on each plate is fixed. An external force is applied to increase the separation of the plates. Where is the additional energy required for this process being stored?

The potential in the field of a dipole is at its maximum along the dipole axis.

Identical 2.5 µC charges are located on the vertices of a square with sides that are 1.0 m in length. What is the electric potential (relative to zero at infinity) at the centre of the square?

The Bohr model of the hydrogen atom states that the single electron can exist only in certain permitted orbits around the proton. The radius of each Bohr orbit is r = n²(0.051 nm), where n = 1, 2, 3,…. Calculate the change in electric potential energy of a hydrogen atom when the electron makes a transition from the n = 2 to the n = 1 orbit. Express your answer in electron volts.