 |
Heating Effects: Joule's Law |
| |
When a potential difference is applied across the ends of a conductor, the free electrons are accelerated and acquire kinetic energy. As the electrons move through, they collide with the positive ions and atoms of the conductor and transfer their kinetic energy to them. |
|
Practical Applications of Joule's Heating |
| |
This heating is inevitable in any electrical circuit. Since the energy lost by the flowing charges ends up as disorderly thermal motion, the phrase 'ohmic dissipation' is also used to describe it. |
|
Chemical Effects of Current |
| |
The phenomenon of electrolysis is an important chemical effect of electric current. In a metallic conductor, the electric current is due to the drifting of free electrons, there is no chemical or physical change, only the generation of heat. |
|
Chemical Effects of Current (Contd...) |
| |
The mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of charge passed through the electrolyte. |
|
Electrochemical Cells |
| |
The fact that chemical reactions produce electrical effects was discovered accidentally in 1791 by Luigi Galwani, professor of anatomy at the University of Bologna, Italy. |
|
Electrochemical cells (Contd...) |
| |
The electrodes used in the cells discussed so far, deteriorate with the passage of current and cannot offer a constant emf indefinitely. However, there was a few cells called standard cells, which can maintain a fairly constant emf over very long periods of time compared to the other cells. |
|
Thermoelectricity |
| |
Thermoelectricity refers to the phenomena that occur at the junctions of dissimilar conductors when a temperature difference exists between the junctions. The same phenomenon occurs within a single conductor too, with the two ends are maintained at different temperatures. |
|
Thermoelectricity (Contd...) |
| |
In 1834, a French scientist Peltier, found an effect that was the converse of the Seebeck effect. |
|
Applications of Thermoelectricity |
| |
These are in the measurement of temperature and in thermoelectric generators and refrigerators. |
|
Summary |
| |
If a current I flows through a potential drop V, the energy lost per second by the drifting charges is VI. In a resistor of resistance R, the loss of energy appears as heat. The rate of heat production P is P = VI = I2R = V2/R and is independent of the direction of current. |
|
Numerical 01 |
| |
A current of 0.50 ampere is passing through a CuSO4 solution. How many Cu++ ions will be deposited on cathode in 10 seconds? |
|
Numerical 02 |
| |
Six lead-acid type of secondary cells, each of emf 20 V and internal resistance 0.015W, are joined in series to provide a supply to a resistance of 8.5W. Determine (i) the current drawn from the supply and (ii) it's voltage. |
|
Numerical 03 |
| |
It is desired to deposit 0.254 kg of copper on the cathode of a copper voltameter. How long will it take to deposit this amount if a steady current of 100 A is maintained? Use the known value of Faraday's constant. Relative atomic mass of copper is 63. 5. |
|
Numerical 04 |
| |
A steady current of 10.0 A is passed through a water voltameter for 300s. Estimate the volume of H2 evolved at standard temperature and pressure. Use the known value of Faraday's constant. Relative molecular mass of H2 is 2.016 and molar volume = 22.4 litres (volume of 1m of an ideal gas at STP). |
|
Numerical 05 |
| |
In a silver-plating system, an electrolysis current of 5.0 A is used for a certain time and 0.5 moles of silver is deposited. How many moles of copper and iron will be deposited in their respective plating system if an electrolysis current of 10.0 A is passed for twice the time for silver plating? |
|
Numerical 06 |
| |
A piece of metal weighting 200 g is to be electroplated with 5% of its weight in gold. If the strength of the available current is 2 ampere, how long would it take to deposit the required amount of gold? |
|
Numerical 07 |
| |
In a given thermocouple, the temperature of the cold junction is 20oC while the neutral temperature is 270oC. Find the temperature of inversion. |
|
Numerical 08 |
| |
The temperature qn (neutral temperature) corresponding to maximum emf. |
|
Numerical 09 |
| |
At room temperature, the thermo emf of a copper constant couple is 40 mV per degree. What is the smallest temperature difference that can be detected with a single such couple and a galvanometer of 100 ohm resistance capable of detecting current as low as 10-6 ampere? |
|
Numerical 10 |
| |
A sensitive microphone cannot withstand currents greater than 0.05A. When connected across a thermocouple of emf 8.5 mV, the current in a very low resistance ammeter placed in series in the circuit reads 34 mA. Calculate the resistance of the microphone. |
