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# Working with electrostatics -

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1.The anode (positive terminal) of an X-ray tube is at a potential of +90 000 V with respect to the cathode (negative terminal).
(a) How much work (in joules) is done by the electric force when an electron is accelerated from the cathode to the anode?

(b) If the electron is initially at rest, what kinetic energy does the electron have when it arrives at the anode?

2.During a particular thunderstorm, the electric potential difference between a cloud and the ground is Vcloud - Vground = 2.2 108 V, with the cloud being at the higher potential. What is the change in an electron's electric potential energy when the electron moves from the ground to the cloud?

3.Two point charges, +4.00 ÂµC and -6.10 ÂµC, are separated by 1.50 m. What is the electric potential midway between them?

4. An equipotential surface that surrounds a +4.2 10-7 C point charge has a radius of 0.25 m. What is the potential of this surface?

5. Two equipotential surfaces surround a +1.20 10-8 C point charge. How far is the 150 V surface from the 75.0 V surface?

6.A spark plug in an automobile engine consists of two metal conductors that are separated by a distance of 0.55 mm. When an electric spark jumps between them, the magnitude of the electric field is 4.8 107 V/m. What is the magnitude of the potential difference V between the conductors?

7.What voltage is required to store 7.5 10-5 C of charge on the plates of a 7.0 ÂµF capacitor?

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#### Solution Preview

1.The anode (positive terminal) of an X-ray tube is at a potential of +90 000 V with respect to the cathode (negative terminal).
(a) How much work (in joules) is done by the electric force when an electron is accelerated from the cathode to the anode?

A unit of energy that is often used when discussing the energy of an atomic particle is the electron volt(eV). Its magnitude is equal to the energy change of an electron when it moves through a potential difference of one volt.

1 eV = 1.6 x 10-19 joules

If an electrons moves through a PD of 90 000volt, the energy is 90 000 eV

which is equal to 90 000 * 1.6 x 10-19 Joule = 1.44 x 10^-14 joule -- Answer

(b) If the electron is initially at rest, what kinetic energy does the electron have when it arrives at the anode?

Mass of the electron = 9.11 x 10^-31 kg
Work done by the field gets converted to the KE of the ...

#### Solution Summary

Practice problems involving electrostatics - well explained asnwers

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