# PHYSICS II ```PHYSICS II - MIDTERM HOMEWORK
A GROUP
12. What is the potential difference and electric potential?
The effects of any charge distribution can be defined in terms of electric field or
electric potential. Since the electrical potential is scalar, it is easier to use than
the electric field, which is a vector field. We can define the electric field as the
force per unit charge. Likewise, it is useful to define electrical potential (or
simply potential) as the electrical potential energy per unit charge.
By definition, the electric potential difference, or voltage, is the difference in
electric potential between the final and the initial position when work is done
upon a charge to change its potential energy.
The electric potential is indicated by the V symbol. The positive test charge q in
the electric field has electric potential energy Ua at point a. At this point,
electric potential Va:
Therefore, the potential difference (Vba) between points a and b will be equal
to the following relation:
Vba= Vb-Va = Ub-Ua
q
When a point charge q moves from point a to point b, we define the change in
electrical potential energy ( Ub-Ua ) as the negative of the work done by the
electrical force.
The electrical potential and potential difference unit are given in joule / coulomb
and volts respectively. So 1W = 1J / C. The potential difference is often called
voltage.
The potential difference Vba can be written as follows, since the difference in
potential energy (Ub-Ua) is equal to the negative of the work Wba when the
charge moves from point a to point b:
Vba = Vb-Va = Ub-Ua = - Wba
q
q
For example, consider two equally but opposite charged parallel plates and the
distance between them is small relative to their width and height. The electric field
will be smooth in most zones (Figure 2).
Figure 2: Work done by the electric field in the
movement of the positive test charge q from a to b
15. What are the Combinations of Capacitors? Explain
- What is a Capacitor?
Capacitors are two-ended circuit elements that store electrical energy as an
electric field. Basically, it is obtained by placing an insulating material
between two conductive plates. The letter C in the circuit and its equations
and unit are represented by Farad (F).
- What does a capacitor do? What is the duty?
Capacitors do not transmit direct current (DC), but have the ability to transmit
alternating current (AC). Thanks to these features, they are used for different
purposes in most circuits. They are used for filtering in power supply circuits,
generating the desired frequency in resonant circuits, and controlling the voltage
and power flow in power transmission lines.
- Structure of the Capacitor
We have said that the capacitor can be created with an insulator located between
two conductors.
The insulating part may be empty or it may also be composed of a dielectric
substance (paper, glass, plastic, ceramic, mica, etc.).
- The Combinations of Capacitors
Like all other two-prong circuit elements, capacitors can either be parallel or
serially connected to electrical circuits.
(i)
Parallel combination of capacitors
If multiple capacitors are connected in parallel, capacitance values are
summed:
(ii)
Series combination of capacitors
In case capacitors are connected in series, the inverse of the
equivalent capacity by multiplication is equal to the sum of the
inverse of each capacity value by multiplication:
18. What is superconductors , and give an exaple.
When the temperature is low below a certain value, materials with zero direct
current and electrical resistances are called superconductors. High conductivity
or zero resistance allows infinite current to flow through the material.
Hundreds of materials turn into superconductors at low temperatures. The
properties of superconductors are not much different from those of metals.
Superconductivity is the state of matter at a critical temperature or under a
critical magnetic field.
- Properties of Superconductor
The superconducting materials show some amazing properties which are
essential for current technology. The research on these properties is still going
on to recognize and utilize these properties in various fields which are listed
below:
-
Infinite Conductivity/ Zero Electric Resistance
Meissner Effect
Transition Temperature/Critical Temperature
Critical Current
Persistent Currents
Super conductive materials can be made from more than 20 metallic elements.
The 27 chemical elements, all metal, are superconductors in atmospheric
pressure, in their own crystal-graphic forms. Commonly known among these
are Aluminum, Tin, Lead, Mercury, Rhenium, Lanthanum and Proctantium. In
addition, 11 elements that are metal and semiconductor like Uranium,
Selenium, Cerium and Silicon are also super conductive under low heat and
high pressure. Although bismuth is not a superconductor in its crystal graphic
form, it can become a superconductor by going into a regular state at very low
temperatures. None of the magnetic elements such as Chrome, Manganese,
Iron, Cobalt and Nickel have superconductivity.
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