As a demonstration, from this we may calculate the potential difference between two points (
A and
B ) equidistant from a point charge
q at the origin, as shown in
[link] .
To do this, we integrate around an arc of the circle of constant radius r between
A and
B , which means we let
$d\overrightarrow{\text{l}}=r\widehat{\phi}d\phi ,$ while using
$\overrightarrow{\text{E}}=\frac{kq}{{r}^{2}}\widehat{\text{r}}$ . Thus,
However,
$\widehat{\text{r}}\xb7\widehat{\phi}=0$ and therefore
${V}_{B}-{V}_{A}=0.$
This result, that there is no difference in potential along a constant radius from a point charge, will come in handy when we map potentials.
What is the highest voltage possible between two plates?
Dry air can support a maximum electric field strength of about
$3.0\phantom{\rule{0.2em}{0ex}}\times \phantom{\rule{0.2em}{0ex}}{10}^{6}\phantom{\rule{0.2em}{0ex}}\text{V/m}\text{.}$ Above that value, the field creates enough ionization in the air to make the air a conductor. This allows a discharge or spark that reduces the field. What, then, is the maximum voltage between two parallel conducting plates separated by 2.5 cm of dry air?
Strategy
We are given the maximum electric field
E between the plates and the distance
d between them. We can use the equation
${V}_{AB}=Ed$ to calculate the maximum voltage.
Solution
The potential difference or voltage between the plates is
(The answer is quoted to only two digits, since the maximum field strength is approximate.)
Significance
One of the implications of this result is that it takes about 75 kV to make a spark jump across a 2.5-cm (1-in.) gap, or 150 kV for a 5-cm spark. This limits the voltages that can exist between conductors, perhaps on a power transmission line. A smaller voltage can cause a spark if there are spines on the surface, since sharp points have larger field strengths than smooth surfaces. Humid air breaks down at a lower field strength, meaning that a smaller voltage will make a spark jump through humid air. The largest voltages can be built up with static electricity on dry days (
[link] ).
An electron gun (
[link] ) has parallel plates separated by 4.00 cm and gives electrons 25.0 keV of energy. (a) What is the electric field strength between the plates? (b) What force would this field exert on a piece of plastic with a
$0.500\text{-}\mu \text{C}$ charge that gets between the plates?
Strategy
Since the voltage and plate separation are given, the electric field strength can be calculated directly from the expression
$E=\frac{{V}_{AB}}{d}$ . Once we know the electric field strength, we can find the force on a charge by using
$\overrightarrow{\text{F}}=q\overrightarrow{\text{E}}.$ Since the electric field is in only one direction, we can write this equation in terms of the magnitudes,
$F=qE$ .
Solution
The expression for the magnitude of the electric field between two uniform metal plates is
$E=\frac{{V}_{AB}}{d}.$
Since the electron is a single charge and is given 25.0 keV of energy, the potential difference must be 25.0 kV. Entering this value for
${V}_{AB}$ and the plate separation of 0.0400 m, we obtain
Note that the units are newtons, since
$1\phantom{\rule{0.2em}{0ex}}\text{V/m}=1\phantom{\rule{0.2em}{0ex}}\text{N/C}$ . Because the electric field is uniform between the plates, the force on the charge is the same no matter where the charge is located between the plates.
A closely wound search coil has an area of 4cm^2,1000 turns and a resistance of 40ohm. It is connected to a ballistic galvanometer whose resistance is 24 ohm. When coil is rotated from a position parallel to uniform magnetic field to one perpendicular to field,the galvanometer indicates a charge
well when you apply a small electric field to a conductor that causes to add a little velocity to charged particle than usual, which become their average speed, that is what we call a drift.
two point charges +30c and +10c are separated by a distance of 80cm,compute the electric intensity and force on a +5×10^-6c charge place midway between the charges
Heat is the condition or quality of being hot While Temperature is ameasure of cold or heat, often measurable with a thermometer
Abdul
Temperature is the one of heat indicators of materials that can be measured with thermometers, and Heat is the quantity of calor content in material that can be measured with calorimetry.
Gamma
the average kinetic energy of molecules is called temperature.
heat is the method or mode to transfer energy to molecules of an object but randomly, while work is the method to transfer energy to molecules in such manner that every molecules get moved in one direction.
Adnan
2. A brass rod of length 50cm and diameter 3mm is joined to a steel rod of the same length and diameter. What is the change in length of the combined rod at 250°c( degree Celsius) if the original length are 40°c(degree Celsius) is there at thermal stress developed at the junction? The end of the rod are free to expand (coefficient of linear expansion of brass = 2.0×10^-5, steel=1.2×10^-5k^1)