1. Name the substance of which the resistance remains almost unchanged by increasing the temperature.

The resistance of manganin wire remains almost unchanged by increasing in temperature.

2. Explain the analog between the flow of charge in a conductor under potential difference with the free fall of a body under gravity.

Here potential energy of body is equivalent to potential, falling body is similar to charge particle, etc. As a body moves from higher potential energy to lower potential energy similarly charge (positive) flows from higher electric potential to lower potential.

3. Differentiate between terminal voltage and emf of a cell.

Emf (electromotive force) of a cell is the potential difference between terminals of cell when no current flows across the cell.  While the terminal voltage of cell is the potential difference across the terminals of cell when current flows in cell as well as in outer circuit.

4. Give four differences between resistance and resistivity of a wire.

Resistance
(i) it is equal to the ratio of V/I in wire connected in a circuit.
(ii) It changes with l or A of wire.
(iii) It opposes the flow of current in conductor.
(iv) It's SI unit is Ohm (Ω).

Resistivity

(i) It is . So does not depend on V or I in wire.
(ii) It does not change with l or A.  It is constant for a material.
(iii) It is the resistance of the wire of the same material of wire whose l = 1 m and A = 1 m²
(iv) It's SI unit is Ω-m.

5. Explain the meaning of term emf, terminal voltage, and internal resistance of a cell.
Consider a circuit as shown in figure below.
              
(i) emf of a cell:  It is the potential difference across the ends of cell when no current flows across the cell.
It is equal the reading of voltmeter in circuit when Key K is open.

(ii) Terminal voltage of cell:  When current flows in cell or circuit, the potential difference across the cell is called terminal voltage of cell.
When K is closed in above circuit then current passes across external resistance 'R' and across the internal resistance 'r' of cell.  Then th reading of voltmeter when key K is closed gives the terminal voltage of cell.

(iii) Internal resistance of cell:  As the ions flow between the electrodes of cell when current is drawn from the cell.  The ions collide each other and with other neutral atoms (like salvant).  So some resistance is offered by movement of ions.  This is the cause of internal resistance of cell.
The resistance (r) offered between the terminals or plate of cell when no current is drawn from the cell is called internal resistance of cell.

6. The V-I graph of two wires A and B are shown in figure, which one will have more resistance and why?
     
  As we know  R = ^V/_I or slope of V-I graph with I axis gives the value of resistance.  As the slope of graph OB is more than OA. So the resistance of wire B is more than A.

7. What is Ohmic resistance? Give one example of an Ohmic resistance.  Draw a graph to show it's current-voltage relationship.  How is the resistance of the resistor determined from the graph?
   
The resistance which obeys the ohms law is called Ohmic resistance or linear resistance.  All metallic conductors, or alloys.  like,iron, copper, silver, nichrome, wires are ohmic resistance.  Diode, riode, transistors, semiconductors are non-ohmic resistance. I-V graph of Ohmic resistance is always straight line for all values of I or V at constant temperature graph passing through origin.
The resistance of conductor from I-V graph can be determining the slope of I-V or V-I graph with I axis.  The resistance of wire whose graph in figure  is .

8. Resistances are connected in parallel.  What can you say about the equivalent resistance is larger or smaller than any individual resistance?
We know that in parallel equivalent resistance R_p is
                     
So Rp is always smaller than any individual resistances connected in parallel.

9. V-I graph for a series combination and for a parallel combination of three resistors is shown in figure.  Which of the two, A or B represents the parallel combination? Give reasons for our answer.
              
When two resistors are connected in series and parallel, the equivalent resistance is smaller in parallel than series combination.
As R = ^V/_I, so if slope of I-V graph with I axis (x axis in figure) is larger then resistance is larger.  As slope of graph B is smaller than A, so resistance of B is smaller than A, so resistance of graph B is in parallel combination.

10. Two resistors are connected with a battery such that
(a) Same current flows in each resistors
(b) Same potential difference across the ends of each resistors
(c) Equivalent resistance is less than any individual resistors
(d) Equivalent resistance is more than any individual resistor.
State how are the resistors are connected in each of the above case.

(a) As in series combination path of current is only one, so the same current will flow in series combination. (Fig. 1)
(b) As we know that in parallel combination, two ends of each resistors are connected at two points A and B in circuit. Potential difference between A and B or across both resistors will be same.  From above discussion the resistors are connected in parallel. (Fig. 2)
                   
(c) In this case resistors are connected in parallel as equivalent resistance in parallel combination is always smaller than any individual.

(d) In this case resistors are connected in series combination, as the equivalent resistance in series combination is always larger than any individual resistor.