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At balance of Wheatstone network the resistors are such that the current through the galvanometer is zero.(Ig = 0) or 

P/Q = R/S 

P, Q, S, R are in cyclic order.

Conservation of energy. 

The resistivity of a conductor increases linearly with increase of temperature and vice versa.

(a) maximum when the battery is connected across 1 cm × 1/2 cm faces. 

(d) If the assertion and reason both are false.

(i) Student B had concentrated in the classroom teaching and also had studied again to remember what was taught.

(ii) H = I₂Rt

(1) Ohmic resistor obeys ohm's law i.e., V/I is constant for all values of V or I; whereas Non-ohmic resistor does not obey ohm's law i.e., V/I is not same for all values of V or I.

(2) In Ohmic resistor, V-I graph is linear in nature whereas in non-ohmic resistor, V-I graph is non-linear in nature.

Correct answer is (b) manganin

Manganin is used for making the standard resistor because its resistivity is quite large and the effect of change in temperature on their resistance is negligible.

Unit of current = \(\frac{Unit\,of\,charge}{Unit\,of\,time}\)

= C/s OR A

(i) Ammeter reading increases

(ii) Intensity of light increases

(iii) As current in circuit increases, intensity of light increases.

(iv) \(\text{I}=\frac{Q}{t}=\frac{2c}{10s}=0.2C/s \)

= 0.2 A

4 r is r ohms and wire is stretched to double its length, then what is its resistance.

B. open and closed the circuit 

Generally fuse wire is made of an alloy of lead and tin because its resistivity is high and melting point is low.

A superconductor is a substance of zero resistance at a very low temperature. Example: Mercury at 4.2 K.

(i) A wire made of tungsten is used for filament of electric bulb because it has a high melting point and high resistivity.

(ii) A nichrome wire is used as a heating element for a room heater because the resistivity of nichrome is high and increase in its value with increase in temperature is high.

The specific resistance of a wire depends only on the material (at a given temperature). Therefore by changing the radius, the specific resistance of copper remains unchanged.

(b) electric field produced by charges accumulated on the surface of wire. 

Data : R =50 C in the right gap, l_x = 40 cm

Now, l_R = 100 – l_X = 100 – 40 = 60 cm

∴ \(\cfrac X{50}\) = \(\cfrac{40}{60}\)

∴ X = 50 × \(\cfrac23\) = \(\cfrac{100}3\) = 33.33 Ω

This is the unknown resistance.

The macroscopic form of Ohm’s Law relates voltage, current and resistance. Ohm’s Law states that the current through an object is proportional to the voltage across it and inversely proportional to the object’s resistance.

V = IR

Heat generated H = I₂ Rt = \(\frac{V^2t}{R}\)

Given, H = 9H

\(\therefore \,\frac{V'^2}{t}=9\times\frac{V^2t}{R}\)

\(\Rightarrow \) V² = 9 x V² \(\Rightarrow \) V' = \(\sqrt{9}\times V\)

\(\therefore \,\,V=3V\)

∴ Potential difference increases by a factor of \(\sqrt{9}\)  i.e., 3.

1. Even if any one of the several bulbs connected in parallel becomes non-functional because of some damage to its filament, the circuit does not break as the current flows through the other paths, and the rest of the bulbs light up. 

2. When several bulbs are connected in parallel, they emit the same amount of light as when they are connected individually in the circuit, while bulbs connected in series emit less light than when connected individually. Hence, streetlights are connected in parallel.

Correct option is: (a) Resistivity

The internal resistance of a cell is the resistance offered by the electrolyte and electrodes in the cell.

The answer is (A) Charge

The answer is (C) Zero

The answer is (C) 4 A

Correct answer is (c) 3.5 Ω

Correct answer is (c) \(\frac{R}{4}\)

Correct answer is (d) 12A

E = 12 V, r = 0.4 Ω, I = ?

Since I = \(\frac{E}{r}\) = \(\frac{12}{0.4}\) = 30 A.

Given E = 10 V, r = 3?, I = 0.5, R = ?

Since V = E – Ir

or V = 10 – 0.5 × 3

or V = 8.5 volt

And R = \(\frac{V}{I}\) = \(\frac{8.5}{0.5}\) = 17 A

Ampere / metre² (A/m²)  

Correct option is: (A) 2 Ω

It is defined as the electric current (I) per unit area (A) taken normal to the direction of current. i.e., j = (I/A) 

Correct option is: (D) 3A

The SI unit of resistivity is ohm-meter (Ω - m).

Ohmic: (d), Non-Ohmic: (a), (b) and (c)

Only for (d) the I-V graph is a straight line or linear while for (a), (b) and (c), the graph is a curve.

The resistivity of a material of a conductor is defined as the resistance offered by a conductor of length 1 m and area of cross-section 1 m² . Its SI unit is ohm × metre (Ω m).

(a) It measure potential in the open circuit.

The unit of emf is Volt

The resistivity of a material is the resistance of a wire of that material of unit length and unit area of cross-section. Its S.I. unit is ohm metre.

The same current flows through each resistor. The effective resistance of the resistors is equal to the sum of their individual resistances. The potential difference between the two extremes of the arrangement is equal to the sum of the potential differences across individual resistors. The effective resistance is larger than each of the individual resistances. This arrangement is used to increase the resistance in a circuit. This type of connection is used in electrical heating equipment like geysers, iron, and hair dryers.

Expression :

R = p (I/A)

p − resistivity

R – resistance

l – length of conductor

A – area of cross-csection

(c) potential difference

• Every atom of a metallic conductor has one or more outermost electrons which are very weakly bound to nucleus.
• These are called free electrons.
• These electrons can easily move from one part of a conductor to its other parts.

The materials which conduct electricity at zero resistance are called Superconductors.

The resistance of these conductors becomes nearly zero if their temperature is decreased up to a certain value close to 0 K. Aluminium is an example of Super Conductor. Superconductors can be used in space missions to increase/ boost the signal strength. They are also used i in the data fibres to increase the speed of data transfer.

With increase of temperature, resistance of conductors increases.