Current Electricity Flashcards
What is the SI unit of charge
Coulomb
What is the definition of current
Current is defined as the rate of flow of charge
What is the SI unit of current
Ampere
Define potential
Potential at a point is defined as the amount of work done for unit charge in bringing a positive test charge from infinity to that point
Define potential difference
The potential difference between two points is equal to the work done Per unit charge in moving the positive test charge from 1.2 other
The relationship between volt Joule and coulomb
One volt is equals to 1 joule per coulomb
State the Ohm’s law
According to the Ohm’s law the current flowing in a conductor is directly proportional to the potential difference applied across its provided that the physical conditions on the temperature of the conductor remains constant
Formula relating to Ohm’s law
V = IR
Define resistance state its unit
The obstruction offered to the flow of current by conductor is called resistance its unit is ohm
Define conductance
Conductance is the reciprocal of resistance
State the limitations of the Ohm’s law
Ohm’s law is obeyed only when the temperature of the conductor remains constant the Ohm’s law does not work in a semiconductor
Differentiate between ohmic resistors and non ohmic resistors give example of such materials
Homemade resistors follow the Ohm’s law non ohmic resistor does not obey the Ohm’s law example of a ohmic resistor is silver iron copper nichrome example of a non ohmic resistor is LED transistor filament of bulb
State the factors affecting the resistance of a conductor
The material of the conductor the length of the conductor and the thickness of the conductor temperature of the conductor where are is directly proportional to length are is indirectly proportional to area of cross section directly proportional to temperature
Define specific resistance and give the formula related to it also state its unit
Specific resistance of a material is the resistance of a wire of that material of unit length and unit area of cross section its unit is ohm metre.
Formula relating it is
R =p * l / a
R=p * l / pi*r²
Define conductivity give its unit
The reciprocal of specific resistance is known as conductivity it is represented by the symbol Sigma its unit is one by ohm metre
Define a fuse wire
It is made up of alloy of lead and tin because its melting point is low it permits current up to its save limit to pass through it but an excessive current merit its so that it blows of and the circuit is broken it is connected to the main wire
Why is alloy of lead and Tin used for making a fuse wire
Alloys of lead and Tin used for making fuse wire because it’s melting point is low and specific resistance is more than that of copper or aluminium so that the resistance of short and thin fuse wire is more than that of the connecting wire
What is used as a filament of an electric bulb and why
A tungsten wire is used because it has a high melting point and it close to provide light without melting
What type of wire is used in heater toaster an ovens and why
Nichrome wire is used because the specific resistance of nichrome high and its resistance increases to a great extent with the increase in temperature
Define superconductor
Superconductor is a substance of zero resistance at a very low temperature
Define EMF and state it’s unit
When no current is drawn from a cell the potential difference produced by the chemical reaction between the terminals of the cell is called electromotive force or EMF
Define The Terminal voltage of a cell
When current is drawn from a cell the potential difference between the electrodes of the cell is known as its terminal voltage
Differentiate between EMF of a cell and terminal voltage of a cell
Book se dekh lo
Factors affecting the internal resistance of a cell
The surface area of the electrodes the distance between the electrodes the natural concentration of the electrolyte the temperature of the electrolyte
Formula for the combination of parallel resistors
1/R = 1/r¹ + 1/ r²…….
State the formula which is used to express the amount of energy spent
W = i²rt
W = vit
Unit = joule (j)
Formula relating to electrical power and its expression
P = vI
P= v²/r
P= i²r
Convert 1 kwh to Joule
1 kwh = 3.6 x 10⁶ joule
1 w h is equals to how many joules
3600 joules
Factors that effect the heating effect of current
1)The amount of current passing through the wire
H o< i²
2)the resistance of the wire
H o< R
3)the time for which current is passed in the wire
H o< t
Therefore, H =( 0.24) i²rt
