Explore topic-wise InterviewSolutions in Current Affairs.

We know I = nqAv_d . In this n and A are positive. Hence the direction of current is determined by the signs of the charge ‘q’ and drift speed v_d.

1. For electrons, q is negative and v_d is positive. Then the product of q and v_d is negative. So the direction of electric current is opposite to the flow of negative charge.

2. For positive charge, the product of q and v_d is positive. Hence, the direction of electric current can be taken as the direction of flow of positive charges.

1) Ammeter : It is used to measure current. 

2) Volt meter: It is used to measure potential difference across the ends of conductor.

3) Rheostat: It varies current in a circuit. 

4) Switch : It is useful to make a circuit or break a circuit. 

5) Cell: It is source of electric energy in the circuit. 

6) Multimeter : It is useful to measure current, voltage and resistance in the circuit.

C) Semiconductors

Correct answer is (B) 4.5 V

Lightning is an electric discharge between two clouds or between cloud and earth.

The materials which can conduct electricity are called conductors. 

Eg : Copper, Silver, Aluminium.

The electrons in the conductor move with a constant average speed called drift speed or drift velocity

Electrical cells can be divided into several categories like primary cell, secondary cell, fuel cell, etc.

• The line wires that are entering the meter have a voltage of 240 V. 
•  The minimum and maximum limit of current that can be drawn from the mains is 5 to 20 A. 
• Thus, the maximum current that we can draw from the mains is 20 A.
• When the current drawn from the mains is more than 20 A, overheating occurs and may cause a fire. This is called overloading. 
• A short circuit is an electrical circuit that allows a current to travel along an unintended path often where essentially no electrical impedance is encountered.

1. A primary cell cannot be charged again. It can be used only once.

2. Dry cells, alkaline cells are different examples of primary cells.

3. Primary cells are low cost and can be used easily. But these are not suitable for heavy loads.

1. The secondary cells are rechargeable and can be reused. 

2. The chemical reaction in a secondary cell is reversible. 

3. Lead acid cell and fuel cell are some examples of secondary cells. 

4. Lead acid battery is used widely in vehicles and other applications which require high load currents. 

5. Solar cells are secondary cells that convert solar energy into electrical energy.

Advantages:

For cells connected in parallel in a circuit, the circuit will not break open even if a cell gets damaged or open.

Disadvantages:

The voltage developed by the cells in parallel connection cannot be increased by increasing number of cells present in circuit.

1. Fuel cells vehicles (FCVs) are electric vehicles that use fuel cells instead of lead acid batteries to power the vehicles. 

2. Hydrogen is used as a fuel in fuel cells. The by product after its burning is water. 

3. This is important in terms of reducing emission of greenhouse gases produced by traditional gasoline fuelled vehicles. 

4. The hydrogen fuel cell vehicles are thus more environment friendly.

1. The cells connected in series produce a larger resultant voltage. 

2. Cells which are damaged can be easily identified, hence can be easily replaced.

i. Current density at a point in a conductor is the amount of current flowing per unit area of the conductor.

Current density, J = \(\frac{I}{A}\)

where, I = Current

A = Area of cross-section

ii. SI unit: A/m²

The direction of the current in a circuit is drawn in the direction in which positively charged particles would move, even if the current is constituted by the negatively charged particles, (electrons), which move in the direction opposite to that the electric field.

1. A rheostat is an adjustable resistor used in applications that require adjustment of current or resistance in an electric circuit. 

2. The rheostat can be used to adjust potential difference between two points in a circuit, change the intensity of lights and control the speed of motors, etc. 

3. Its resistive element can be a metal wire or a ribbon, carbon films or a conducting liquid, depending upon the application. 

4. In hi-fi equipment, rheostats are used for volume control.

Correct answer is (B) to continuously change the resistance in any arbitrary manner and there by alter the current.

The answer is (d) 1 Ω

Maximum resistance is obtained when resistors are connected in series.

R= 1/5 + 1/5 + 1/5 +1/5 + 1/5

= 5/5

= 1Ω

Correct option is  A) series

C) X is true, Y is false

Correct option is  B) P/2

Correct option is  D) volt

Correct option is  A) W/q

Correct option is  A) I = Q/t

D) Electric current is random motion of free electrons in a conductor.

C) both A and B

Yes. With the help of the formula W = F_e l, we can find the work done by the electric force.

D) The positive ions of the metal conductor are in motion.

From an electric field set up throughout the conductor.

Correct answer is (D) 125 : 15 : 1

(D) increase in the rate of collisions between the current carriers and the vibrating atoms of the conductor.

Correct answer is (B) 1.8 V

(A) relaxation time decreases.

Correct option is: (A) 10/9 Ω

Correct option is: (D) oxides of metals

Correct option is: (D) all of the above

An ammeter is used to measure electric current.

Correct option is: (A) 10^-3 °C

Drift velocity and current density will change as it depends upon area of cross-section whereas current will remain constant.

Correct answer is (A) 2

Yes, lightning is a live example.

C) Lightning between two clouds

 1. Electrical conduction in a conductor is due to mobile charge carriers (electrons).

2. These conduction electrons are free to move inside the volume of the conductor.

3. During their random motion, electrons collide with the ion cores within the conductor. Assuming that electrons do not collide with each other these random motions average out to zero.

4. On application of an electric field E, the motion of the electron is a combination of the random motion of electrons due to collisions and that due to the electric field \(\overrightarrow{E}\).

5. The electrons drift under the action of the field \(\overrightarrow{E}\) and move in a direction opposite to the direction of the field \(\overrightarrow{E}\).

In this way electrons in a conductor conduct electricity.

Electromotive force (emf) is defined as the work done by the chemical force to move unit positive charge from negative terminal to positive terminal of the battery.

At a particular temperature, the resistance (R) of a conductor of uniform cross section is

i. directly proportional to its length (l),

i.e., R ∝ l ……….. (1)

ii. inversely proportional to its area of cross section (A),

R ∝ \(\frac{1}{A}\) ……….. (1)

From equations (1) and (2),

R = ρ\(\frac{l}{A}\)

where ρ is a constant of proportionality and it is called specific resistance or resistivity of the material of the conductor at a given temperature.

iii. Thus, resistivity is given by,

ρ = \(\frac{RA}{l}\)

B) The values of resistivity of alloys are smaller than those of metals

A voltmeter is used to measure potential difference or emf across an electric device like a battery.

\(\frac{V}{I}\) is constant. This constant is called the resistance of the conductor.

The filament of an electric bulb is made of tungsten.