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Which of the following materials has a large number of free electrons in it?
The substances which have many free electrons and offer very low resistance are called conductors.
The substances which cannot pass a current under normal conditions are known as insulators. The resistance of an insulator is usually high. Insulators have no free electrons.
Two bulbs of rating 230 V, 60 W and 230 V, 100 W are connected in parallel across supply mains. Identify the correct statement.
Power dissipation in a lamp,
Since both bulbs are rated at the same voltage, we can say that resistance of each bulb is inversely proportional to its rated power. Therefore, the resistance of 60 W bulb (R60) is greater than the resistance of 100 W (R100) bulb.
Since lamps connected in parallel, the voltage across the both bulb is same.
The power dissipated across 60 W lamp,
The power dissipated across 100 W lamp,
As R60 > R100, the power dissipated across 100 W is greater than 60 W.
Hence 100 W bulb will glow brighter in parallel connection.
The temperature coefficient of resistance of a wire is 0.00125 per °C. At 300K its resistance is 1 ohm. The resistance of the wire will be 2 ohms at
The resistance of most of the metals increases in a linear way with temperature as shown and can be represented by the equation:
RT = R0(1 + αT)
RT = Resistance at a temperature T
R0 = Resistance at 0°C
α = Temperature coefficient of the resistance
α = 0.00125 per °C
R300K = 1 Ω, i.e.
T = 300 - 273 = 27°C
1 = R0(1 + α × 27) ---(1)
Let the resistance be 2 Ω for some temperature T. We can write:
2 = R0(1 + α T) ---(2)
(1) ÷ (2)
(1 + α T) = 2 (1 + α × 27)
α (T - 54) = 1
T - 54 = 800
T = 854°C
T = 854 + 273 = 1127 K
Which of the following is the dimension of power?
The dimensional formula is defined as the expression of the physical quantity in terms of mass, length, time and ampere.
Power – It is defined as rate of doing work.
∴ P = W/t
Where, P = power, W = work done and t = time.
Dimensional formula of work (W) = [ML2T-2]
Dimensional formula of time (t) = [T1]
∴ The dimensional formula of power P is [ML2T-3].
An ideal current source should have:
Ideal voltage source: An ideal voltage source have zero internal resistance.
Practical voltage source: A practical voltage source consists of an ideal voltage source (VS) in series with internal resistance (RS) as follows,
An ideal voltage source and a practical voltage source can be represented as shown in the figure:
Ideal current source: An ideal current source has infinite resistance. Infinite resistance is equivalent to zero conductance. So, an ideal current source has zero conductance.
Practical current source: A practical current source is equivalent to an ideal current source in parallel with high resistance or low conductance.
Ideal and practical current sources are represented as shown in the below figure:
Determine the power delivered by the current source in the figure below:
Power delivered by current source is given by
P = I2 Req
I = current provides by current source
Req = equivalent resistance
Applying the current division rule, we can write:
Also, the equivalent resistance across the current source is:
Now, the power delivered by the current source will be:
In series combination of resistance, the current through each resistance is _________.
The measurement of the opposition of the flow of electric current through a conductor is called resistance of that conductor. It is denoted by R.
There are mainly two ways of the combination of resistances:
1. Resistances in series:
2. Resistances in parallel
A network of resistors is connected to a 16 V battery with an internal resistance of 1 Ω, as shown in the figure. Compute the equivalent resistance of the network.
The circuit after removing the voltage source
Req = Rt = 3 + 2 + 2 = 7 Ω
The equivalent resistance of the network is 7 Ω.
Siemens is the S.I unit of _________.
If an ideal voltage source and ideal current source are connected in series, the combination
In a series circuit, the current flows through all the elements is the same. Thus, any element connected in series with an ideal current source is redundant and it is equivalent to an ideal current source only.
In a parallel circuit, the voltage across all the elements is the same. Thus, any element connected in parallel with an ideal voltage source is redundant and it is equivalent to an ideal voltage source only.
The resistance of a coil is 600 Ω. The temperature coefficient at 20°C is 0.1%. What will be the value of resistance at 50°C?
Resistance of the material at temperature 'T' °C is given by
RT = RT1[1 + α(T - T1)]
RT1 = Resistance at temperature 'T1' °C
α = Temperature coefficient of resistance
T = 50°C
T1 = 20°C
RT1 = 600 Ω
α = 0.1% = 0.001
Now the value of resistance at 50°C can be calculated as
RT = 600[1 + 0.001(50 - 20)]
RT = 600[1 + 0.001(30)]
RT = 600 + 18
RT = 618 Ω
Which of the following expression correctly represents Kirchhop's Voltage Law (KVL) for the given circuit diagram?
Kirchhoffs Voltage Law (KVL):
∴ According to KVL,
V1 + V2 + V3 + V4 + V5 = 0
The circuit diagram given in the question can be modified as
Now by applying KVL in the above circuit, we get
5 + 7 - Vx = 0
∴ - 5 - 7 + Vx = 0
The total effective resistance of the practical capacitor is made of which of the following parameter:
Equivalent Circuit for a Capacitor:
The total effective resistance is made up of the following resistances:
Fig. above shows the equivalent circuit of a capacitor. We can replace all the resistances with a single equivalent series resistance Rse as shown in Fig below.
The value of Rse is such that I2R loss in it is equal to the total loss in the capacitor.
Constant voltage source is
Which one of the following is used as an active device in electronic circuits?
A network element that is absorbing power i.e. energy delivered to the element is positive then the element is a passive element.
Example: resistor, inductor, and diode.
A network element that is delivering power i.e. energy delivered to the element is negative then the element is an active element.
Example: Op-amp, generator, SCR, etc.
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