# Case Study Chapter 3 Current Electricity Class 12 Physics

Please refer to below Case Study Chapter 3 Current Electricity Class 12 Physics. These Case Study Questions Class 12 Physics will be coming in your examinations. Students should go through the Chapter 3 Current Electricity Case Study based questions in their Class 12 Physics CBSE, NCERT, KVS book as this will help them to secure more marks in upcoming exams.

## Case Study Based Questions Physics Class 12 – Chapter 3 Current Electricity

The flow of charge in a particular direction constitutes the electric current. Current is measured in Ampere. Quantitatively, electric current in a conductor across an area held flowing across that area per unit time. Current density at a point in a conductor is the ratio of the current at that point in the conductor to the area of cross section of the conductor of that point. The given figure shows a steady current flows in a metallic conductor of non uniform cross section. Current density depends inversely on area, so, here J1 >J2 as A1 < A2.

Question. What is the current flowing through a conductor, if one million electrons are crossing in one millisecond through a cross-section of it?
(a) 2.5 × 10–10 A
(b) 1.6 × 10–10 A
(c) 7.5 × 10–9 A
(d) 8.2 × 10–11 A

B

Question. SI unit of electric current is
(a) C s
(b) N s–2
(c) C s–1
(d) C–1 s–1

C

Question. A steady current flows in a metallic conductor f non-uniform cross-section. Which of these quantities is constant along the conductor?
(a) Electric field
(b) Drift velocity
(c) Current
(d) Current density

C

Question. A constant current I is flowing along the length of a conductor of variable cross-section as shown in the figure. The quantity which does not depend upon the area of cross-section is

(a) electron density
(b) current density
(c) drift velocity
(d) electric field

A

Question. When a current of 40 A flows through a conductor of area 10 m2, then the current density is
(a) 4 A/m2
(b) 1 A/m2
(c) 2 A/m2
(d) 8 A/m2

A

If two or more capacitors are connected in series, the overall effect is that of a single (equivalent) capacitor having the sum total of the plate spacing of the individual capacitors. If two or more capacitors are connected in parallel, the overall effect is that of a single equivalent capacitor having the sum total of the plate areas of the individual capacitors

Question. Capacity can be increased by connecting capacitors in:
(a) Parallel
(b) Series
(c) Both (a) and (b)
(d) None the these

A

Question. Three capacitors having a capacitance equal to 2F, 4F and 6F are connected in parallel. Calculate the effective parallel capacitance:
(a) 10 F
(b) 11 F
(c) 12 F
(d) 13 F

C

Question. When capacitors are connected in the series …………… remains the same.
(a) Voltage
(b) Capacitance
(c) Charge
(d) Resistance

C

Question. The plates of a parallel plate capacitor are 10 cm apart and have an area equal to 2m2. If the charge on each plate is 8.85 × 10–10 C the electric field at a point
(a) between the plates will be zero.
(b) outside the plates will be zero.
(c) between the plates will change from point to point.
(d) between the plates will be 25NC – 125NC–1.

B

Question. Four 10F capacitors are connected in series the equivalent capacitance is
(a) 1.5 F
(b) 2.5 F
(c) 3.5 F
(d) 4.5 F

B

According to Ohm’s law, the current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor i.e., l ∝ V ⇒ V/I = R, where R is resistance of the conductor. Electrical resistance of a conductor is the obstruction posed by the conductor to the flow of electric current through it. It depend upon length, area of cross-section nature of material and temperature of the conductor. We can write, R ∝ l/A or R = ρ (l/A)  where ρ is electrical resistivity of the material of the conductor.

Question. Dimensions of electric resistance is
(a) [ML2 T–2 A2]
(b) [ML2 T–3 A–2]
(c) [M-1 L–2 T–1 A]
(d) [M–1 L2 T2 A–1]

B

Question. If 1 μA current flows through a conductor when potential difference of 2 volt is applied across its ends, then the resistance of the conductor is
(a) 2 × 106 Ω
(b) 3 × 105 Ω
(c) 1.5 × 105 Ω
(d) 5 × 107 Ω

A

Question. Specific resistance of a wire depends upon
(a) length
(b) cross-sectional area
(c) mass
(d) none of these

D

Question. The slope of the graph between potential difference and current through a conductor is
(a) a straight line
(b) cure
(c) first curve then straight line
(d) first straight line then curve

A

Question. The resistivity of the material of a wire 1.0 m long, 0.4 mm in diameter and having a resistance of 2.0 ohm is
(a) 1.57 × 10–6 Ω m
(b) 5.25 × 10–7 Ω m
(c) 7.12 × 10–5 Ω m
(d) 2.55 × 10–7 Ω m

D

Temperature Dependance of Resistivity. The of a conductor at temperature tºC is given by Rt = R0 (1 + αt) where Rt is the resistance at tºC and α is the characteristics constants of the material of the conductor. Over a limited range of temperatures, that is not too large. The resistivity of a metallic conductor is approximately given by ρt = ρ0 (1 + αt) where α is the temperature coefficient of resistivity. Its unit is K–1 or ºC–1. For metals, α is positive i.e., resistance increases with rise in temperature. For insulators and semiconductors, α is negative i.e., resistance decreases with rise in temperature.

Question. Fractional increase in resistivity per unit increase in temperature is defined as
(a) resistivity
(b) temperature coefficient of resistivity
(c) conductivity
(d) drift velocity

B

Question. The material whose resistivity is insensitive to temperature is
(a) silicon
(b) copper
(c) silver
(d) nichrome

D

Question. The temperature coefficient of the resistance of a wire is 0.00125 per ºC. At 300 K its resistance is 1 ohm. The resistance of wire will be 2 ohms at
(a) 1154 K
(b) 1100 K
(c) 1400 K
(d) 1127 K

D

Question. The temperature coefficient of resistance of an alloy used for making resistors is
(a) small and positive
(b) small and negative
(c) large and positive
(d) large and negative

A

Question. For a metallic wire, the ratio V/I (V = applied potential difference and I = current flowing) is
(a) independent of temperature
(b) increases as the temperature rises
(c) decreases as the temperature rises
(d) increases or decreases as temperature rises depending upon the metal

B

Grouping of Cells. A single cell provides a feeble current. In order to get a higher current in a circuit, we often use a combination of cells. A combination of cells is called a battery. Cells can be joined in series, parallel or in mixed way. Two cells are said to be connected in series when negative terminal of one cell is connected to positive terminal of the other cell and so on. Two cells are said to be connected in parallel if positive terminal of each cell is connected to one point and negative terminal of each cell connected to the other point. In mixed grouping of cells, a certains number of identical cells are joined in series, and all such rows are then connected in parallel with each other.

Question. To draw the maximum current form a combination of cells, how should the cells be grouped?
(a) Parallel
(b) Series
(c) Mixed grouping
(d) Depends upon the relatives values of internal and external resistances

D

Question. The total emf of the cells when n identical cells each of emf ε are connected in parallel is
(a) n∈
(b) n2ε
(c) ε
(d) ∈/n

C

Question. 4 cells each of emf 2 V and internal resistance of 1 Ω are connected in parallel to a load resistor of 2 Ω . Then the current through the load resistor is
(a) 2 A
(b) 1.5 A
(c) 1 A
(d) 0.888 A

D

Question. If two cells out of n number of cells each of internal resistance ‘r’ are wrongly connected in series, then total resistance of the cell is
(a) 2nr
(b) nr – 4r
(c) nr
(d) r

B

Question. Two identical non-ideal batteries are connected in parallel. Consider the following statements.
I. The equivalent emf is smaller than either of the two emfs.
II. The equivalent internal resistance is smaller than either of the two internal resistances.
(a) Both I and II are correct.
(b) I is correct but II is wrong.
(c) II is correct but I is wrong.
(d) Both I and II are wrong.