current electricity Flashcards
the phase between drift velocity/steady current and electric fiel or potential
pi
180 degrees
Ohm’s law can be applied to
- A. A.C
- B. D.C
both
The specific resistance of a conductor increases with:
Increase in temperature
Because specific resistance is independent of dimensions of a wire.
The resistance of a wire is 11 Ohm. Its length is increased by 10% stretching. The new resistance will be
2n + n2/100 ; n=10%
210% + (1010/100)
20 + 1 = 21 %
11 + 0.21 -> 11.2
The slope of current-voltage graph gives us:
Conductance
1/R
The deviation of I-V graph from the straight line is due to
increase in temp and increase in R
what is the practical unit of power
horse power
what is the cgs unit of power
Erf sec-1
Under what condition is the e.m.f. of a cell equal to its terminal voltage?
when no current is drawn from cell
The potential difference between the terminals of a battery will equal the emf of the battery when there is no current in the battery. At this time, the potential drop across the internal resistance is zero. This only happens when there is no load placed on the battery that includes measuring the potential difference with a voltmeter. The terminal voltage will exceed the emf of the battery when current is driven backward through the battery, in at its positive terminal and out at its negative terminal.
Heat produced by current I in the wire of resistance R is?
Power = I2R. To convert power to energy we need to multiply it with time. So heat produced (energy) = I2Rt.
Two electric bulbs rated P1 watt V volts, and P2 watt V volts are connected in series and applied across V volts. The total power will be
Power will be (p1 + p2) watt when connected in parallel and P1P2 / (P1 + P2) when connected in series.
Increase in the temperature for a substance results in?
Resistance may increase or decrease with the increase in temperature. For conductors it increase and for semi-conductors and insulators it decreases.
The potential difference between the terminals of battery in open circuit is 2.2 V. When it is connected across a resistance of 5.0 ohm, the potential falls to 1.8 V. What is the current of the battery?
when you draw current from a battery, the terminal voltage decreases. For example: when you start your car with the headlights on, they dim while you’re cranking the engine. This is why the model for a battery is an ideal voltage source (voltage constant regardless of output current) in series with the “internal resistance Ri “. Thus, the “open circuit voltage = 2.2V is the value of the ideal voltage source upstream from Ri. When you connect 5Ω across the terminals and read 1.8V you know the current in the 5Ω is
I = V/R = 1.8V/5Ω = 0.36A
Therefore that 0.36A Ri must be the cause of the voltage drop from 2.2V to 1.8V
=2.2-1.8 = 0.4V
0.4V = 0.36 × Ri
Ri = 0.4/0.36 = 40/36 = 10/9 Ω = 1.11111…..Ω
For a metallic wire, the ratio of voltage to corresponding current is?
For a metallic wire with increase in temperature the resistance of the wire increases hence the ratio of voltage to corresponding current increases with rise in temperature
E is EMF of a battery. What will be the potential drop across terminals an external resistance R = r (internal resistance) is connected across it?
E = Ir + Ir
of r = R
E = 2IR
E = 2V
V = E/2
Internal resistances is the resistance offered by
electrolyte
The resistance is due to electrolyte present between the two electrodes of the cell is called the internal resistance of cell.
The maximum output delivered to a load resistance is
E2 / 4r
Which one is used to determine the internal resistance of the cell
Potentiometer can be used as:
i. Potential divider
ii. To measure the unknown EMF of the cell
iii. To compare the unknown EMFs of two cells
iv. To measure the internal resistance of cell
Identify the type of application where heating effect of current is used:
when an electric current is passed through a conductor, it generates heat due to the hindrance caused by the conductor to the flowing current. The work done in overcoming the hindrance to the current generates heat in that conductor.
The heating effect of electric current is used in the following applications:
Electric Bulb: In an electric bulb, the filament of bulb gives light because of heating effect of electricity. The filament of bulb is generally made of tungsten metal; having melting point equal to 3380°C.
Electric iron: The element of electric iron is made of alloys having high melting point. Electric heater and geyser work on the same mechanism.
Electric fuse: Electric fuse is used to protect the electric appliances from high voltage; if any. Electric fuse is made of metal or alloy of metals, such as aluminium, copper, iron, lead, etc. In the case of flow of higher voltage than specified, fuse wire melts and protects the electric appliances.
An electric iron is marked 20 volts 500 W. The units consumed by it in using it for 24 hours will be
12 kwH
500 * 24/1000
Potentiometer practically draws
you can’t measure current by using potentiometer because potentiometer draws zero current under balanced condition. When the potentiometer is used in the circuit for measurement then it doesn’t draw any current. It can only be used to find either the internal resistance of a cell or the ratio of the emf (potential difference) of the two cells.
Resistance of a super conductor is
Superconductors are materials that carry electrical current with exactly zero electrical resistance. This means you can move electrons through it without losing any energy to heat.
The electrical analogue of mass in electricity is:
As per mechanical-electrical analog, displacement is analogous to charge and force analogous to voltage.
It can be concluded that electrical analog of mass is inductance.
The resistance of a conductor at an absolute zero is
0
Thermocouples generates energy at the cost of
heat energy
A thermocouple is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the Seebeck effect, and this voltage can be interpreted to measure temperature.
Temperature coefficient of thermistors
negative
hermistors with high negative temperature coefficient are very accurate for measuring low temperature especially near 10K.
the change in a resistance of metallic conductor below 0?
linear
formula for power dissipated in cables
P = I^2 R
