Physics Test 197

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Physics Test 197

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Question 1
4 / -1

The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A, is

A
Independent of the distance between the plates

B
Linearly proportional to the distance between the plates

C
Proportional to the square root of the distance between the plates

D
Inversely proportional to the distance between the plates

Solution

For isolated capacitor, charge Q= constant.

Electrostatic force,
Question 2
4 / -1

Suppose the charge of a proton and an electron differ slightly. One of them is -e, the other is (e+Δe). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then Δe is of the order of

[given ma of hydrogen mh = 1.67×10⁻²⁷kg]

A
10⁻²³C

B
10⁻³⁷C

C
10⁻⁴⁷C

D
10⁻²⁰C

Solution
Question 3
4 / -1

A capacitor of 2 μF is charged as shown in the diagram. When the switch S is turned to position 2, the percentage of its stored energy dissipated is

A
75%

B
80%

C
0%

D
20%

Solution
Question 4
4 / -1

An electric dipole is placed at an angle of 30° with an electric field intensity 2 × 105NC⁻¹.It experiences a torque equal to 4 N m. The charge on the dipole, if the dipole length is 2 cm, is

A
8 mC

B
2 mC

C
5 mC

D
7 mC

Solution
Question 5
4 / -1

People living at sea level have around 5 million RBC per cubic millimeter of their blood whereas those living at an altitude to 5400 metres have around 8 million. This is because at high altitude

A
People eat more nutritive food, therefore more RBCs are formed

B
People get pollution-free air to breath and more oxygen is available

C
Atmospheric O₂ level is less and hence more RBCs are needed to absorb the required amount of O₂ to survive

D
There is more UV radiation which enhances RBC production.

Solution

At high altitudes composition of air remains almost same as at sea level, but density (barometric pressure) of air gradually decreases due to which arterial pO₂ is also decreased (hypoxemia). High altitudes has complex conditions to which human body has to acclimatize. Number of red blood cells per unit volume of blood is likely to be higher in a person living at high altitudes. This is in response to the air being less dense at high altitude. More number of red blood cells are needed to trap O₂ from rarefied air having low pO₂ (partial pressure of oxygen).
Question 6
4 / -1

An electric bulb is rated 220 V–100 W. The power consumed by it when operated on 110 V will be

A
50 W

B
75 W

C
40 W

D
25 W

Solution
Question 7
4 / -1

A (100 W, 200 V) bulb is connected to a 160 V power supply. The power consumption would be

A
125 W

B
100 W

C
80 W

D
64 W

Solution

Power = 100 W, Voltage = 200 V

The resistance of bulb = V² / P = 200 x 200 / 100 = 400Ω

When the bulb is connected across 160 V

Current in bulb = 160 / 400 A,

Power consumption = VI = 160 × 160 / 400 = 64 W
Question 8
4 / -1

The relation between current and drift velocity is

A
I = nev_d

B
I/A = nev_d

C
IA=nev_d

D
I = nv_dA / e

Solution

As we know, I = neAv_d

Therefore, I/A = nev_d
Question 9
4 / -1

A conductor wire having 10²⁹ free electrons carries a current of 20 A. If the cross-section of the wire is 1 mm², then the drift velocity of electrons will be

A
6.25 × 10⁻³ m s⁻¹

B
1.25 × 10⁻⁵ m s⁻¹

C
1.25 × 10⁻³ m s⁻¹

D
1.25 × 10⁻⁴ m s⁻¹

Solution
Question 10
4 / -1

The current passing through the ideal ammeter, in the circuit given below, is

A
1.25 A

B
0.5 A

C
0.75 A

D
1 A

Solution

To calculate the equivalent resistance for the ammeter, the resistors of 2 Ω and 2 Ω are in parallel with each other and then the whole circuit has 3 resistances in series.

Now, internal resistance of the battery, that is 1 Ω, resistance of 2 Ω and resistance R = 1 Ω, are all in series.

R_eq for series is the sum of all the resistances.

∴ R_eq = 1 Ω + 2 Ω + 1 Ω = 4 Ω

Hence current, I = V / R

I = 4 / 4 = 1 A