Earth as a Magnet, Static and Current Electricity
Earth as a Magnet, Static and Current Electricity MCQ Questions
7.
Which of the following materials is a good insulator?
Approach
The question asks to identify a good insulator from the given options. An insulator is a material that does not allow heat or electricity to pass through it easily. We need to evaluate each option based on its electrical conductivity properties.
Step-by-step
- Understand Insulators: An insulator is a material with very high electrical resistance, meaning it strongly opposes the flow of electric current. This is due to the absence of free electrons that can move easily through the material.
- Evaluate Copper: Copper is a metal known for its excellent electrical conductivity. It is widely used in electrical wiring.
- Evaluate Aluminum: Aluminum is also a metal and a good conductor of electricity, though not as good as copper. It is used in overhead power lines and electrical components.
- Evaluate Glass: Glass is a non-metallic, amorphous solid. It has a very high electrical resistivity and is commonly used as an electrical insulator in various applications, such as in light bulbs, electrical components, and as a dielectric in capacitors.
- Evaluate Silver: Silver is the best electrical conductor among all metals. It has the lowest resistivity and is used in high-performance electrical contacts and components.
- Conclusion: Based on the properties, glass is the only material among the options that is a good insulator.
Correct Option: C) Glass is a non-metallic material with very high electrical resistance, making it an excellent insulator. It does not allow electric current to flow through it easily.
Incorrect Options
- A) Copper — Copper is a metal and an excellent conductor of electricity, widely used in electrical wiring.
- B) Aluminum — Aluminum is also a metal and a good conductor of electricity, often used in power transmission lines.
- D) Silver — Silver is the best electrical conductor among all metals, known for its very low electrical resistance.
8.
Which type of circuit has only one path for the flow of electric current?
ANSWER :
A. Series circuit
Approach
The question asks to identify the type of electrical circuit that offers only one path for the flow of electric current. We need to recall the fundamental characteristics of different circuit configurations: series, parallel, and combination circuits.
Step-by-step
- Understand Series Circuits: In a series circuit, components are connected end-to-end along a single path. This means that the current flowing through each component is the same because there is no alternative route for the current to take. If one component breaks, the entire circuit is interrupted, and current stops flowing.
- Understand Parallel Circuits: In a parallel circuit, components are connected across the same two points, creating multiple paths for the current to flow. The voltage across each component is the same, but the current divides among the paths. If one component breaks, current can still flow through the other parallel paths.
- Understand Combination Circuits: A combination circuit (or series-parallel circuit) incorporates both series and parallel connections within the same circuit. It will have sections with a single path and sections with multiple paths for current.
- Understand Complex Circuits: This is a general term often used to describe circuits that are not simple series or parallel, but it's not a distinct fundamental type like series or parallel. It usually refers to combination circuits or circuits with multiple sources and loads.
- Evaluate the options: Based on the definitions, a circuit with "only one path for the flow of electric current" perfectly describes a series circuit.
Correct Option:
A) Series circuit — In a series circuit, all components are connected sequentially, forming a single continuous loop. Consequently, the electric current has only one path to follow through all the components. If this path is broken at any point (e.g., by a switch opening or a component failing), the entire circuit becomes open, and current ceases to flow.
Incorrect Options
- B) Parallel circuit — A parallel circuit provides multiple distinct paths for the electric current to flow. The total current from the source divides among these paths, and each path can operate independently to some extent.
- C) Combination circuit — A combination circuit consists of both series and parallel arrangements of components. Therefore, it will have sections with multiple paths for current, not just one.
- D) Complex circuit — This is a broad term and typically refers to circuits that are not simple series or parallel, often implying a combination of both. Such circuits inherently have multiple paths for current in at least some parts.
9.
What is the resistance of a superconductor at very low temperatures?
Approach
The question asks about the resistance of a superconductor at very low temperatures. Understanding the definition and properties of superconductors is key to answering this question.
Step-by-step
- Define Superconductor: A superconductor is a material that, when cooled below a certain critical temperature (\(T_c\)), exhibits exactly zero electrical resistance and expels magnetic fields (Meissner effect).
- Electrical Resistance: Electrical resistance is a measure of the opposition to the flow of electric current. In normal conductors, resistance decreases with decreasing temperature but never reaches zero.
- Behavior at Low Temperatures: For a superconductor, as the temperature drops below its critical temperature, the electrons pair up (Cooper pairs) and can move through the material without scattering, leading to zero resistance. This is a defining characteristic of superconductivity.
- Conclusion: Therefore, at very low temperatures (below their critical temperature), superconductors have zero electrical resistance.
Correct Option: C) Zero. Superconductors are defined by their property of having exactly zero electrical resistance when cooled below a specific critical temperature.
Incorrect Options
- A) High — This is incorrect. High resistance is characteristic of insulators or poor conductors, not superconductors at low temperatures.
- B) Low — While resistance decreases as temperature drops in normal conductors, for superconductors, it drops to exactly zero, not just 'low'. 'Low' is not precise enough to describe this unique property.
- D) Variable — This is incorrect. Once a material enters the superconducting state (below \(T_c\)), its resistance is consistently zero, not variable.
10.
Which of the following is used to store electric charge?
Approach
The question asks to identify the electronic component used for storing electric charge. We need to recall the primary function of each given option.
Step-by-step
- Understand the function of a Capacitor: A capacitor is a passive two-terminal electrical component that stores electrical energy in an electric field. It consists of two conductive plates separated by a dielectric (insulating) material. When a voltage is applied across the plates, an electric charge accumulates on them. The relationship between charge (\(Q\)), capacitance (\(C\)), and voltage (\(V\)) is given by \(Q = CV\).
- Understand the function of an Inductor: An inductor is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. It typically consists of a coil of wire.
- Understand the function of a Resistor: A resistor is a passive two-terminal electrical component that implements electrical resistance in a circuit. Its primary function is to oppose the flow of electric current, converting electrical energy into heat.
- Understand the function of a Diode: A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance to current in one direction, and high (ideally infinite) resistance in the other. It does not store charge in the way a capacitor does.
- Compare functions: Based on the primary functions, the capacitor is explicitly designed to store electric charge.
Correct Option: A) A capacitor is an electronic component specifically designed to store electric charge in an electric field. This stored charge can then be released back into the circuit when needed.
Incorrect Options
- B) Inductor: An inductor stores energy in a magnetic field, not directly as electric charge. Its primary function is to oppose changes in current.
- C) Resistor: A resistor dissipates electrical energy as heat and limits current flow; it does not store electric charge.
- D) Diode: A diode allows current to flow in one direction and blocks it in the other. It is used for rectification and switching, not for storing electric charge.
11.
A device that converts mechanical energy into electrical energy is called
Approach
The question asks to identify the device that converts mechanical energy into electrical energy. We need to recall the fundamental functions of each given option.
Step-by-step
- Analyze the conversion: The core requirement is a device that takes mechanical energy as input and produces electrical energy as output. This process is known as electromagnetic induction, where motion (mechanical energy) in a magnetic field generates an electric current.
- Evaluate Option A (Generator): A generator works on the principle of electromagnetic induction. It uses mechanical energy (e.g., from a turbine powered by steam, water, or wind) to rotate coils of wire within a magnetic field, thereby inducing an electric current. Thus, it converts mechanical energy into electrical energy.
- Evaluate Option B (Motor): A motor performs the opposite function of a generator. It takes electrical energy as input and converts it into mechanical energy (rotational motion).
- Evaluate Option C (Battery): A battery stores chemical energy and converts it into electrical energy through chemical reactions. It does not convert mechanical energy.
- Evaluate Option D (Resistor): A resistor is a passive electrical component that opposes the flow of electric current. It converts electrical energy into heat energy (Joule heating). It does not convert mechanical energy into electrical energy.
Correct Option:
A) Generator — A generator is specifically designed to convert mechanical energy (from various sources like turbines, engines, etc.) into electrical energy based on the principle of electromagnetic induction.
Incorrect Options
- B) Motor — A motor converts electrical energy into mechanical energy.
- C) Battery — A battery converts chemical energy into electrical energy.
- D) Resistor — A resistor converts electrical energy into heat energy.
12.
Which of the following is a unit of electric power?
Approach
The question asks to identify the unit of electric power from the given options. To answer this, we need to recall the definitions and standard units of various electrical quantities.
Step-by-step
- Understand Electric Power: Electric power is the rate at which electrical energy is transferred or converted. It is a measure of how much work an electric circuit can do in a given amount of time.
- Recall the formula for Electric Power: Electric power (\(P\)) can be defined in several ways, including:
- \(P = V \times I\) (Voltage multiplied by Current)
- \(P = I^2 \times R\) (Current squared multiplied by Resistance)
- \(P = V^2 / R\) (Voltage squared divided by Resistance)
- Identify the standard unit of Power: The standard international (SI) unit for power (including electric power) is the Watt.
- Evaluate the options: We will check each option to see if it corresponds to the unit of electric power.
Correct Option:
D) Watt
The Watt (\(W\)) is the SI unit of power, defined as one joule per second (\(1 \text{ J/s}\)). In electrical terms, one Watt is the power produced when one Ampere of current flows through an electrical potential difference of one Volt (\(1 \text{ W} = 1 \text{ V} \times 1 \text{ A}\)). Therefore, Watt is the correct unit for electric power.
Incorrect Options
- A) Ohm — The Ohm (\(\Omega\)) is the SI unit of electrical resistance. Resistance is a measure of the opposition to the flow of electric current. It is defined by Ohm's Law as the ratio of voltage to current (\(R = V/I\)).
- B) Volt — The Volt (\(V\)) is the SI unit of electric potential difference (also known as voltage or electromotive force). It represents the energy per unit charge, defined as one joule per coulomb (\(1 \text{ V} = 1 \text{ J/C}\)).
- C) Ampere — The Ampere (\(A\)) is the SI unit of electric current. It is a measure of the rate of flow of electric charge, defined as one coulomb per second (\(1 \text{ A} = 1 \text{ C/s}\)).
