Electricity - MCQ Test (22-11-2017) - Class 10 MCQ

Metals are electropositive in nature and are therefore, good conductors of electricity. Quartz is a chemical compound consisting of one part silicon and two parts oxygen (SiO₂). It is the most abundant mineral found in Earth's surface. Its unique properties make it one of the most useful natural substances. It has electrical properties and heat resistance that make it valuable in electronic products. Mica has superior electrical properties as an insulator. Rubber is also an insulator.

Electrical resistivity (also known as resistivity) is an intrinsic property of a material that quantifies how strongly a given material opposes the flow of electric current. Resistivity of a material varies with temperature. Resistivity of a conductor increases with increase in temperature. When a wire is stretched, its material remains the same and hence, the resistivity remains the same.

The total charge that flows through the electric device, Q = I x t
or Q = (1.5 A) x (4 hours)
or Q = (1.5 A) x (4 x 60 x 60 sec)
or Q = 21600 C

The rate at which electric energy is lost (dissipated) or consumed in a thermal device due to resistance R is given by P = VI or P = I²R = V²/R

Q = n x e. Therefore, number of electrons present in one coulomb of charge, 

Nichrome is used for electric wire heater since it is an alloy of nickel, chromium, manganese and iron, and does not oxidise easily at high temperatures. It has a resistivity of 100×10⁻⁶Ωm

Electrons are negatively-charged particles. The object losing electrons gains positive charge. The object gaining electrons gains negative charge.

The current will be same in all the bulbs. In a series combination of resistors, the same current flows through each resistor. The current is the same in every part of the circuit.

The drift velocity is the average velocity that a particle, such as electrons, attains in a material due to a steady electric field. It can also be referred to as axial drift velocity.

An ammeter has a low resistance since it is always connected in series in an electrical circuit. If it is connected in parallel, a high current will flow through it and it is likely to burn out.

The path of motion of free electrons in a metal is zig-zag. The normal motion of “free” electrons in a conductor is random, with no particular direction or speed.

Manganin is an alloy of copper, manganese and nickel. It typically contains 86% copper, 12% manganese, and 2% nickel. It was first developed by Edward Weston in 1892 improving upon his Constantan. Manganin wire is used in the manufacture of resistors.

A Rheostat is an electrical instrument used to control current in a circuit by varying the resistance. The resistance can be decreased or increased with the help of a rheostat.

The two ebonite rods rubbed on fur repel each other because the electrical properties of the two ebonite rods are similar to each other. Both the rods acquire like charges when rubbed on fur. Ebonite is a very hard rubber obtained by vulcanizing natural rubber for prolonged periods. The rods gain electrons when rubbed on fur and acquire negative charge.

Positive charges move from higher potential to lower potential. Negative charges move from lower potential to higher potential. Free electrons inside a conductor move towards the region of higher potential.

B and C are correct. An ammeter is a low resistance device. A semiconductor material has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. As the temperature increases, their resistance decreases.
A and D are incorrect. A neutron is a sub-atomic particle that has no charge. One µA is equal to 10^-6 A. An ampere is a bigger unit. Micro-ampere (µA) is a smaller unit.

Resistivity of Nichrome at room temperature is (100—150) × 10⁻⁸ ohm metre.

A light bulb has a higher resistance. A toaster produces more heat than a light bulb since it draws a higher current from the same source when connected in parallel. According to Joule's law of heating, the heat produced in a resistor is directly proportional to the square of the current for a given resistance, directly proportional to the resistance for a given current and directly proportional to the time for which the current flows through the resistor. H = I²Rt.

The potential difference between two points - point  A and point B - is the work done in moving a unit charge from point A to point B.

Resistance (R) of a conductor at a given temperature:

• is directly proportional to the length (l)
• is inversely proportional to the area of cross-section (a)
• depends on the nature of the material (ρ)

R=ρ×l/a

According to Joule's law of heating, the heat produced in a resistor is directly proportional to the square of the current for a given resistance, directly proportional to the resistance for a given current and directly proportional to the time for which the current flows through the resistor. H = I²Rt

According to Joule's law of heating, the heat produced in a resistor is directly proportional to the square of the current for a given resistance, directly proportional to the resistance for a given current and directly proportional to the time for which the current flows through the resistor. H = I²Rt
When a constant current 'I' is applied for a time of 't' seconds, the heat produced can be increased to four times by increasing the resistance to four times the original value. H₁ = I²Rt ; H₂ = I²(4R)t ; H₂ = 4H₁

Many conductors do not obey ohm's law. They are known as non-ohmic conductors. For such conductors, the graph between potential difference and current is not a straight line passing through the origin. Vacuum tubes, semiconductor diodes, transistors, liquid electrolytes, thermistors, etc are examples of such conductors.

Charges given in A, B and C are possible. 1.6×10⁻¹⁹C is the amount of charge on a proton or an electron. This is the minimum charge that any particle will have.

Electrons are not consumed in an electrical circuit. Energy provided to an electric circuit moves electrons through gadgets like electric iron, bulbs, etc.

Energy consumed E = P (in kW) x t (in hours) = 0.2 x 2 = 0.4 kWh

The main feature of Constantan and Manganin is their resistivity, which is constant over a wide range of temperatures. Manganin wire is used in the manufacture of resistors, particularly ammeter shunts, because of its virtually zero temperature coefficient of resistance value and long term stability.

Tungsten is remarkable for its robustness, especially the fact that it has the highest melting point of all the elements discovered. It has a melting point of 3380^oC.

Light from a bathroom bulb gets dimmer for a moment, when the geyser is switched on. A geyser has a higher power rating and draws a large current from the mains when it is switched on.
Insulators do not conduct charges; they have high resistivity.

The two wires are of the same length and the same radius; hence, their resistance will be proportional to their resistivity. Nichrome wire is an alloy of nickel, chromium, manganese and iron and has a resistivity of 100 x 10^-6ohm-m. Copper has a low resistivity of 1.62 x 10^-8 ohm-m. Therefore, the Nichrome wire will get heated first. According to Joule's law of heating, the heat produced in a resistor is directly proportional to the resistance for a given current. H = I²Rt. Also, Nichrome does not oxidise easily at high temperatures. That is why, it is commonly used in electrical heating devices like electrical iron, heaters, etc.