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I have a question based on current as we all know that current flows due to the movement of electrons in substance. Now suppose a conductor having electrons randomly in motion so we study that current flow due to flow of electrons in a substance so this have to produce electric current. Then why a substance (conductor) doesn’t make current; but when connected to a socket it give current..
The resistances of 2 bulbs are in the ratio 1:2.if they are joined in series,find the ratio of the energy consumed by the 2 bulbs?
When connected in series, the same current flows through each of the resistors. Therefore, the energy dissipated is directly proportional to their resistances. That is, the ratio of energy dissipated will nbe same as the ratio of resistances. (1:2)
Some important points to remember
- The resistance of a conductor does not change when the current through it is changed or the voltage across it is changed. When current is changed, the voltage across it is also changed so that the ratio V/I = R
- The value of resistance changes if the dimensions (length or area of cross section of the conductor) changes or the temperature changes.
- When the dimensions of a conductor is changed, the resistance changes, but the resistivity does not change.
- When temperature is changed, both resistivity as well as resistance changes.
- At room temperature (27 oC) resistance of a heating element is 100 ohm. What is the temperature of the element if the resistance is found to be 117 ohm. Given, temperature coeff. of resistance of the material is 1.70 x 10 -14 oC-1
- The ends of a resistance are connected to 19 cells in series, each of resistance 0.1 ohm. The current is found to be 2A. The number of cells is reduced to 15 and an extra resistance of 9.5 ohm is connected in series to the given resistance. The current becomes half. Find the given resistance and the emf of each cell.
- In a potentiometer arrangement a cell of emf 1.25 V gives a balance point at 35 cm length of the wire. If the cell is replaced by another cell, the balance point shifts to 63 cm. What is the emf of the second cell?
E1= 1.25 V
l1 = 35 cm
l2 = 63 cm
E1/E2 = l1/l2
E2 = l2E1/l1
E2 = 63 x 1.25/35
E2 = 2.25 V (Ans)
A Problem for Practice
A storage battery of emf 8 V and internal resistance 0.5 ohm is charged by 120V dc supply using a resistor 15.5 ohm in series. What is the terminal voltage of the battery during charging?
(Try to solve this problem and post your responses as comment to this post)
Hint: During charging; V = E +Ir
“What is meant by potential difference?”
“Potential Difference between two points is the difference in Potential between the two points and is equal to the work done per unit charge ion carrying a positive test charge from one point to another against the electric field and without any acceleration”