Lecture PowerPoints Chapter 17 Physics: …hep0.okstate.edu/flera/phys1214/Ch17_Lecture.pdf17.6 Potential Due to Electric Dipole; Dipole Moment Or, defining the dipole moment p = Ql,
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Lecture PowerPoints
Chapter 17 Physics: Principles with Applications, 7th edition
A charge Q is in an electric field. What happens if that charge is replaced by a charge 2Q?
a) The electric potential doubles, but the electric potential energy stays the same;
b) The electric potential stays the same, but the electric potential energy doubles;
c) Both the electric potential and electric potential energy double;
d) Both stay the same
Example 1
• An electron acquires 6.95×10−16 J of kinetic energy when it is accelerated by an electric field from plate A to plate B. What is the potential difference between the plates?
In general, the electric field in a given direction at any point in space is equal to the rate at which the electric potential decreases over distance in that direction.
17.2 Relation between Electric Potential and Electric Field
17.6 Potential Due to Electric Dipole; Dipole Moment
Or, defining the dipole moment p = Ql, [C×m]
In many molecules, even though they are electrically neutral, electrons tend to be close to one of the atoms. This results in a separation of charge within a molecule.
Such molecules have a dipole moment and are called polar molecules – they play an important role in a molecular biology.
• A 2.5 mF capacitor is charged to 746 V and a 6.8 mF capacitor is charged to 562 V. These two capacitors are then disconnected from their batteries. Next positive plates are connected to each other and negative plates are connected to each other. What will be the potential difference across each and the charge across each?
A charged capacitor stores electric energy by separating + and – charges. The energy stored is equal to the work done to charge the capacitor.
The net effect of charging a capacitor is to remove charge from one plate and add it to the other plate. This is what the battery does when connected to a capacitor. As more charge is transferred, work is needed to move charge against the increasing voltage V.
Energy stored in a capacitor can be considered as energy stored in the electric field. The energy density, defined as the energy per unit volume, is the same no matter the origin of the electric field:
The electric energy stored per unit volume in any region of space is proportional to the square of the electric field in that region.
The sudden discharge of electric energy can be harmful or fatal. Capacitors can retain their charge indefinitely even when disconnected from a voltage source—be careful!
Heart defibrillators use electric discharge to “jump-start” the heart when its beats become irregular, and can save lives.
Digital signals use binary numbers to represent numerical values. In a binary number, each digit or bit has only two possibilities, 0 or 1. Each byte of 8 bits allows 28 = 256 possibilities.
17.10 Digital; Binary Numbers; Signal Voltage When an analog signal is converted to digital (Analog-to-Digital Converter, or ADC), the digital signal might look like blue line. In order to convert an analog signal to digital, the signal must be sampled. A higher sampling rate reproduces the signal more precisely.