[2 Mark Questions]

Question 12 Marks

Find the effective resistance between A and B in the given circuit.

Answer

Effective resistance in parallel combination $3 \Omega$ and $2 \Omega$CCCCCCCCCCCCCC
$\frac{1}{ R _{ p }}=\frac{1}{ R _1}+\frac{1}{ R _2}=\frac{1}{3}+\frac{1}{2}=\frac{2+3}{6}=\frac{5}{6} \Omega$
$R_P=\frac{6}{5}=1.2 \Omega$
$\underbrace{1.2 \Omega \quad 2 \Omega}$
$R_{ S }=R_1+R_2=1.2+2=3.2 \Omega \text {. }$

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Question 22 Marks

Calculate the resistivity of the material of wire $10$ m long, $0.4$ mm in diameter and having a resistance of $20\ Ω.$

Answer

$I =10 m ; d =0.4 mm =0.4 \times 10^{-3} m $
$r =0.2 \times 10^{-3} m $
$R =20 \Omega$
Resistivity (or) specific resistance of a material
$\rho =\frac{ RA }{l}=\frac{ R \times \pi r^2}{l} $
$ =\frac{20 \times 3.14 \times\left(0.2 \times 10^{-3}\right)^2}{\text 10} $
$ =6.28 \times 0.04 \times 10^{-6} $
$\rho =2.513 \times 10^{-8} \Omega m$

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Question 32 Marks

How many electrons pass through a lamp in one minute, if the current is 300 mA?

Answer

$\begin{aligned} I =300 mA & =300 \times 10^{-3} A \\ t & =1 \text { minute }=60 s \\ e & =1.6 \times 10^{-19} C \\ I & =\frac{q}{t}=\frac{n e}{t} \text \\ n & =\frac{ I t}{e}=\frac{300 \times 10^{-3} \times 60}{1.6 \times 10^{-19}}=1.125 \times 10^{20}\end{aligned}$

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Question 42 Marks

Show that one ampere is equivalent to a flow of 6.25 × 1018 elementary charges per second.

Answer

$I =1 A , t =1 s , e =1.6 \times 10^{-19} C$
$q = ne $
$I =\frac{q}{t}=\frac{n e}{t}$
Number of electrons, $n=\frac{ I t}{e}=\frac{1 \times 1}{1.6 \times 10^{-19}}=6.25 \times 10^{18}$.

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Question 52 Marks

What is the unit of resistance? Define its unit of resistance is ohm.

Answer

Resistance of a conductor is said to be one ohm if a current of one ampere flows through it when a potential difference of one volt is maintained across its ends.
$
1 ohm =\frac{1 \text { volt }}{1 \text { amphre }}
$

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Question 62 Marks

Define Volt.

Answer

The potential difference between two points is one volt, if one joule of work is done in moving one coulomb of charge from one point to another against the electric force.
$
1 \text { volt }=\frac{1 \text { joule }}{1 \text { coulomb }}
$

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Question 72 Marks

Define electric potential difference.

Answer

The electric potential difference between two points is defined as the amount of work done in moving a unit positive charge from one point to another point against the electric force.

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Question 82 Marks

Distinguish electric power and electric energy?

Answer

Electric Power	Electric Energy
Electric Power is defined as the rate of doing work	It is the capacity to do electric work
P = VI	E = P × t
Unit is watt	Unit is joule (or) [kWh]

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Question 92 Marks

Differences between series and parallel circuit?

Answer

Criteria	Series	Parallel
Equivalent resistance	More than the highest resistance	Less than the lowest resistance
Amount of current	Current is less as effective resistance is more	Current is more as effective resistance is less
Switching ON/OFF	If one appliance is disconnected, others also do not work.	If one appliance is disconnected, others will work independently.

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Question 102 Marks

Define specific resistance electrical conductivity? Give its unit.

Answer

The reciprocal of electrical resistivity of a material is called its electrical conductivity.
$
\sigma=\frac{1}{\rho}
$
Its unit is ohm ${ }^{-1}$ metre $^{-1}$. It is also represented as mho metre ${ }^{-1}$.

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Question 112 Marks

Define electrical resistivity? Give its unit.

Answer

The electrical resistivity of a material is defined as the resistance of a conductor of unit length and unit area of cross – section.
Its unit is ohm metre.

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