Question 11 Mark
Draw a graph between potential difference (V) and current (I) according Ohm's law.
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Question 21 Mark
What is internal resistance of a cell?
Question 31 Mark
Write difference between terminal voltage and electromotive force of a cell.
Question 41 Mark
Electromotive forces of two cells are $\varepsilon_1$ and $\varepsilon_2$ and their internal resistances are $r_1$ and $r_2$ Both cells are joined in lateral combination. Write equivalent electromotive force of this combination.
Answer
View full question & answer→$\varepsilon_{e q}=\frac{\varepsilon_1 r_2+\varepsilon_2 r_1}{r_1+r_2}$
Question 51 Mark
A negligibly small current is passed through a wire of length 15 m and uniform cross-section 6.0 x 10-7 m2 ,and its resistance is measured to be 5.0 Ω. What is the resistivity of the material at the temperature of the experiment?
Answer
View full question & answer→Given:
Length of the wire, $l=15 m$
Area of cross-section of the wire, $A =6.0 \times 10^{-7} m^2$
Resistance of the wire, $R =5.0 \Omega$
Resistivity of the wire, $\rho=$ ?
We know$\rho=\frac{RA}{l}$
$=\frac{5.0 \times 6.0 \times 10^{-7}}{15 m}=\frac{30 \times 10^{-7}}{15}$
$=2 \times 10^{-7} \Omega m$
Length of the wire, $l=15 m$
Area of cross-section of the wire, $A =6.0 \times 10^{-7} m^2$
Resistance of the wire, $R =5.0 \Omega$
Resistivity of the wire, $\rho=$ ?
We know$\rho=\frac{RA}{l}$
$=\frac{5.0 \times 6.0 \times 10^{-7}}{15 m}=\frac{30 \times 10^{-7}}{15}$
$=2 \times 10^{-7} \Omega m$
Question 61 Mark
The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4 $\Omega$, what is the maximum current that can be drawn from the battery?
Answer
View full question & answer→Maximum current can be taken from the battery when external resistance in the circuit is zero
Maximum current, $\quad I =\frac{ E }{ R +r}$
Putting $R =0$
$I _{\max }=\frac{ E }{0+r}=\frac{ E }{r}$
or$I_{\max }=\frac{12 V}{0.4 \Omega}=30 A$
Maximum current, $\quad I =\frac{ E }{ R +r}$
Putting $R =0$
$I _{\max }=\frac{ E }{0+r}=\frac{ E }{r}$
or$I_{\max }=\frac{12 V}{0.4 \Omega}=30 A$
Question 71 Mark
Why there is internal resistance in any cell?
Answer
View full question & answer→It is because the motion of ions inside the cell is obstructed by the collisions with the atoms of the electrolyte.
Question 81 Mark
The algebraic sum of currents at a point in an electric circuit is zero, then what is that point known as?
Answer
View full question & answer→Junction
Question 91 Mark
What is the condition for maximum sensitivity of Wheatstone bridge?
Answer
View full question & answer→All the four resistances joined in its four arms should be of same order.
Question 101 Mark
On what conservation laws are Kirch off's first and second laws based?
Answer
View full question & answer→First law on the conservation of law and second law on the conservation of energy.
Question 111 Mark
A current of I ampere is flowing in a conductor. The same current is flowing in a semiconductor also. If temperature of both is increased, what will be effect on the current flowing through them?
Answer
View full question & answer→In conductor, the magnitude of current will decrease but in semiconductor it will increase.
Question 121 Mark
Under what condition is terminal voltage at the ends of a secondary cell is equal to its electromotive force?
Answer
View full question & answer→When cell is in open circuit or when no current is flowing from the cell in the external circuit.
Question 131 Mark
If potential difference across the ends of any conductor in increased from V to 3 V, then how will drift velocity of electron change?
Answer
View full question & answer→Since, drift velocity,
$v_d=\left(\frac{e \tau}{m l}\right) V$
$\Rightarrow \quad v_d \propto V$times.
On doing V to 3 V , drift velocity will become three
$v_d=\left(\frac{e \tau}{m l}\right) V$
$\Rightarrow \quad v_d \propto V$times.
On doing V to 3 V , drift velocity will become three
Question 141 Mark
How does conductance of a semi-conductor changes with increase in temperature?
Answer
View full question & answer→Since, resistance of a semiconductor decreases with increase in temperature, so its conductance $\left(\frac{1}{R}\right)$ with increase in temperature.
Question 151 Mark
If length of a wire of resistivity p is stretched to three times, then what will be new resistivity?
Answer
View full question & answer→The new resistivity p will remain. Since, the resistivity depends on the substance and not on the shape and size.
Question 161 Mark
A resistor R is joined across a cell of internal resistance r and electromotive force E. Now a potentiometer measures potential difference V across the ends of the cell. Write an expression for r in terms of E, V and R.
Answer
View full question & answer→$r=\left[\frac{E}{V}-1\right] R$
Question 171 Mark
V-I graph of wire of any metal at two different temperatures $T _1$ and $T _2$ are shown in the given figure. Which of the two temperatures is higher and why?
Answer
View full question & answer→Slope of V-I graph is $\frac{V}{I}=$ R. It means lesser the slope: more is the magnitude of resistance. Resistance of any metal increases with increase in temperature. Hence, $T_1>T_2$.
Question 181 Mark
Resistivities of two conductors of same metal shown in the figure are $\rho_1 \Omega m$ and $\rho_2 \Omega m$. Write the ratio of $\rho_1$ and $\rho_2$ will be $1: 1$.
Answer
View full question & answer→We know that the resistivity depends on the substance of the conductor. Here both the conductors are of same substance. Hence the ratio of $\rho_1$ and $\rho_2$ will be $1: 1$.
Question 191 Mark
We cannot determine the internal resistance of an accumulator cell by Wheatstone bridge. Why?
Answer
View full question & answer→The internal resistance of an accumulator cell is less than one ohm, so it cannot be determined with the help of Wheatstone bridge.
Question 201 Mark
Write mathematical form of Krichhoff's junction rule.
Answer
View full question & answer→$\Sigma i=0$ which means that the algebraic sum of all currents meeting at a junction is zero.
Question 211 Mark
What is the magnitude of electromotive forces of batteries used in any closed electric circuit?
Answer
View full question & answer→It is equal to the sum of potential differences produced across the ends of resistors joined in the circuit.
Question 221 Mark
When Wheatstone bridge is said to be balanced?
Answer
View full question & answer→When there is no deflection in cell and galvanometer both on closing the keys of both that is no current flows in its arm, it is said to be balanced.
Question 231 Mark
Are Kirchhoff's laws applicable on both AC and DC circuits?
Answer
View full question & answer→Yes
Question 241 Mark
Can internal resistance of car batteries be determined with the help of Wheatstone bridge?
Answer
View full question & answer→No, because internal resistance of car batteries is very less.
Question 251 Mark
What is the importance of Kirchhoff's laws related to electric circuit?
Answer
View full question & answer→In complex electric circuits where more than one electromotive force sources are present, Ohm's law cannot be applied. In such circuits, only Kirchhoff's laws can be applied.
Question 261 Mark
What is parallel combination of cells?
Answer
View full question & answer→Such a combination of cells in which like terminals of all cells are joined together is known as parallel combination of cells.
Question 271 Mark
Write the condition when terminal voltage and electromotive force of any battery are equal.
Answer
View full question & answer→When the internal resistance of a battery is zero or it is in open circuit which means no current is taken from it.
Question 281 Mark
What is the effect on specific conductance of any electrolyte with increase in temperature?
Answer
View full question & answer→With increase in temperature, due to increase in number of ions in electrolyte and their mobility, its specific conductance will increase due to decrease in its resistivity.
Question 291 Mark
What is the effect of increase of temperature on relaxation time? What is the effect on drift velocity of free electron?
Answer
View full question & answer→Both relaxation time and drift velocity increases on increasing the temperature.
Question 301 Mark
What is the value of I in the given figure?
Answer
View full question & answer→According to Kirchhoff's law
$0.7 A+1.2 A=0.1 A+0.8 A+ I$
$\Rightarrow \quad 1.9 A=0.9+ I$
$\Rightarrow \quad I =1.9-0.9$
$\Rightarrow \quad I =1.0 A$ Ans.
$0.7 A+1.2 A=0.1 A+0.8 A+ I$
$\Rightarrow \quad 1.9 A=0.9+ I$
$\Rightarrow \quad I =1.9-0.9$
$\Rightarrow \quad I =1.0 A$ Ans.
Question 311 Mark
What is the effect on the magnitudes of resistance and resistivity of deforming the shape of a substance?
Answer
View full question & answer→Resistance will change as it depends on physical condition of the substance. Resistivity will remain the same because it depends on the nature of the substance.
Question 321 Mark
What is the charge on flowing current in a conducting wire?
Answer
View full question & answer→Zero. The amount of charge which enters the wire, same amount of charge moves out of the wire.
Question 331 Mark
What is the concept of direction of electric current ?
Answer
View full question & answer→The direction of electric current in metals is taken opposite to the direction of free electrons. In liquids and gases, the direction is taken in the direction of positive ions or opposite to the direction of negative charge carriers.
Question 341 Mark
What is the relation between drift velocity and relaxation time of free electrons in metals?
Answer
View full question & answer→$v_d=\left(\frac{e \tau}{m l}\right) V$
Question 351 Mark
What is mobility? Write its expression also.
Answer
View full question & answer→For any conductor, ratio of drift velocity and electric field inside the conductor remains constant at the given temperature. This constant quantity is known as mobility $(\mu)$ of charge carrier (electron)
$ \text { mobility }(\mu)=\frac{\text { drift velocity }}{\text { electric field }}=\frac{e \tau}{m} $
$ \text { mobility }(\mu)=\frac{\text { drift velocity }}{\text { electric field }}=\frac{e \tau}{m} $
Question 361 Mark
State Ohm's law
Answer
View full question & answer→If physical conditions remain constant, the magnitude of current flowing in a conductor is proportional to the potential difference V across the ends of the conductor.
$V \propto I$
$V = IR$
Where R is a constant.
$V \propto I$
$V = IR$
Where R is a constant.
Question 371 Mark
On joining resistances in parallel, the total resistance of the circuit will increase or decrease?
Answer
View full question & answer→Value of total resistance decreases.
Question 381 Mark
What is the effect on the resistance due to increase in the temperature?
Answer
View full question & answer→Due to small change in temperature, there is no change in thermal expansion but for more change in temperature of resistance, ratio of length and area of crosssection will decrease which will affect the resistance.
Question 391 Mark
Write corresponding values for X and Y on decreasing the length to half of conductors X and Y where $X =4$ and $Y =4 \Omega$ and $Y =48 \times 10^{-8} \Omega m$.
Answer
View full question & answer→We know that resistance is proportional to the length $R \propto l$
When length is reduced to half, magnitude of resistance will also become half which means $X ^{\prime}=2 \Omega$
Resistivity does not depend on length or area of crosssection of wire, hence $Y ^{\prime}=48 \times 10^{-8} \Omega m$.
When length is reduced to half, magnitude of resistance will also become half which means $X ^{\prime}=2 \Omega$
Resistivity does not depend on length or area of crosssection of wire, hence $Y ^{\prime}=48 \times 10^{-8} \Omega m$.
Question 401 Mark
With increase in temperature, will the drift velocity of free electrons in a metallic conductor increase or decrease?
Answer
View full question & answer→$v_d=\frac{e V \tau}{m l}$
$\Rightarrow \quad v_{ d } \propto \tau$ and $\tau=\frac{\lambda}{ V _{ ms }}$
hence drift velocity will increase.
$\Rightarrow \quad v_{ d } \propto \tau$ and $\tau=\frac{\lambda}{ V _{ ms }}$
hence drift velocity will increase.
Question 411 Mark
Define current density. State its unit.
Answer
View full question & answer→Magnitude of current flowing in the perpendicular direction of unit area of cross-section is known as current density J.
Current density $J =\frac{ i }{\Delta S }$, where, $\Delta S$ is area of cross-section.
If the direction of flow of charge is inclined at an angle with the perpendicular, then
current density, $J=\frac{i}{\Delta S \cos\theta}$ or $I=\vec{J} \cdot \overrightarrow{\Delta S}$
Current density $J =\frac{ i }{\Delta S }$, where, $\Delta S$ is area of cross-section.
If the direction of flow of charge is inclined at an angle with the perpendicular, then
current density, $J=\frac{i}{\Delta S \cos\theta}$ or $I=\vec{J} \cdot \overrightarrow{\Delta S}$
Question 421 Mark
Give definition of ampere in electric current.
Answer
View full question & answer→If one coulomb of charge passes through any conductor in one second, then magnitude of current flowing in the conductor is one ampere. 1 A = 1 coulomb/1 second.
Question 431 Mark
If a graph is drawn between different potential differences applied across the ends of the conductor and their corresponding values of current, then what type of graph is obtained?
Answer
View full question & answer→It is obtained in the form of a straight line.
Question 441 Mark
Drift velocity is inversely proportional to what? and it does not depend on what?
Answer
View full question & answer→Drift velocity is inversely proportional to applied potential difference on the conducting rod and drift velocity of electrons in the conductor does not depends on length of the conductor.
Question 451 Mark
$\tau$ is known as relaxation time. State factors on which it depends and factors on which it does not depend
Answer
View full question & answer→Magnitude of relaxation time depends on the nature of the conducting substance and it does not depend on the magnitude of electric field.
Question 461 Mark
Define resistivity. Write its unit.
Answer
View full question & answer→Resistance of a conductor of length 1 m and area of cross-section 1 m² is equal to its resistivity. Its unit is ohm metre or ohm cm.
Question 471 Mark
If temperature of an electric conductor (i) increases (ii) decreases, how the relaxation time of electrons changes in it?
Answer
View full question & answer→(1) decreases (ii) increases.
Question 481 Mark
What is the necessary condition for Ohm's law to be effective ?
Answer
View full question & answer→Physical conditions should remain constant (temperature, length, area of cross-section).
Question 491 Mark
In metals, what is the order of magnitude of number of free electrons, their thermal velocities, pursuit velocity and relaxation time?
Answer
View full question & answer→Number of free electrons $=10^{29}$, thermal velocity $10^5= m / s$, pursuit velocity $=10^{-4} m / s$, relaxation time $=$ $10^{-14} s$