Physics Chapter on Resistance Units

Questions and Answers

What is the power of the immersion water heater when operated at 200 V with a current of 6.8 A?

800 W

2000 W

1360 W (correct)

680 W

What is the total energy consumed by the immersion water heater in 30 days if it operates for 3 hours a day?

122400 W

3600 W

1224 kWh

122.4 kWh (correct)

What is the cost of operating the immersion water heater for one month at Rs 5.00 per unit?

Rs 1000

Rs 300

Rs 612 (correct)

Rs 500

What does the heating effect of current refer to?

The generation of heat due to resistance in the wire Signup and view all the answers

Which wire heats more when electric current is passed through it for the same duration?

Nichrome wire Signup and view all the answers

What happens to the resistance of a conductor when its temperature increases?

Resistance increases. Signup and view all the answers

Why does the electric source eventually get exhausted when supplying current?

Due to the constant supply of energy for resistance Signup and view all the answers

Which of the following statements is true regarding resistivity?

Resistivity is constant for a given material. Signup and view all the answers

When the diameter of a conductor is doubled, how does its resistance change?

Resistance becomes one-fourth. Signup and view all the answers

What happens to the resistance of a wire when it is heated?

It increases significantly Signup and view all the answers

What is the SI unit of conductivity?

Siemen Signup and view all the answers

What is the role of electrical resistance in the heating effect?

To dissipate energy as heat Signup and view all the answers

Which materials are generally classified as semiconductors?

Germanium and silicon Signup and view all the answers

What is the role of a rheostat in an electric circuit?

To vary the resistance of the circuit. Signup and view all the answers

What characteristic of resistivity distinguishes it from resistance?

Resistivity does not change with shape. Signup and view all the answers

What is the effect of temperature on the resistance of alloys like nichrome?

Resistance is unaffected by temperature. Signup and view all the answers

What is the unit of resistance?

Ohms Signup and view all the answers

What effect does increasing the cross-sectional area of a conductor have on its resistance?

Decreases resistance Signup and view all the answers

Which factor does NOT influence the resistance of a conductor?

Temperature of the surrounding environment Signup and view all the answers

If a conductor is longer than another but has the same cross-section, which of the following statements is true?

The longer conductor offers greater resistance. Signup and view all the answers

What is the relationship between the length of a conductor and the current flowing through it?

Shorter conductors allow more current to flow. Signup and view all the answers

Why is it advisable to use thick conducting wires in wiring?

They minimize resistance and energy loss. Signup and view all the answers

In terms of resistance, which of the following pairs of conductors is true?

A thicker wire has lower resistance than a thinner wire, irrespective of length. Signup and view all the answers

What happens to current when the length of the conductor increases?

Current decreases. Signup and view all the answers

What is the formula for calculating electric power?

P = VI Signup and view all the answers

If an appliance rated at 40 W is operating at 220 V, what is the current drawn?

0.18 A Signup and view all the answers

What is 1 kilowatt hour (kWh) equivalent to in joules?

3.6 × 10^6 J Signup and view all the answers

How is electric power defined?

The rate at which energy is consumed Signup and view all the answers

Which of these is the correct unit for electric power?

Watt (W) Signup and view all the answers

What is the relationship between voltage (V), current (I), and resistance (R) as per Ohm’s Law?

V = IR Signup and view all the answers

If an appliance has a current draw of 0.45 A at 220 V, what is its rated power?

100 W Signup and view all the answers

Which of the following appliances has the highest power rating based on the list provided?

Electric heater Signup and view all the answers

What material is commonly used for the filament in electric bulbs to ensure longevity?

Tungsten Signup and view all the answers

What happens to the filament in a bulb when electrical current passes through it?

It starts to emit light due to high temperature. Signup and view all the answers

Why is it advisable to avoid directly touching heating devices?

They can cause severe burns if touched. Signup and view all the answers

How does a fuse protect electrical devices?

By melting and breaking the current path during excess current. Signup and view all the answers

What is a drawback of traditional electric bulbs compared to compact fluorescent lamps (CFLs)?

Traditional bulbs waste electricity in the form of heat. Signup and view all the answers

What is typically the role of a power transformer in electrical power systems?

To step voltage up or down for electricity transmission. Signup and view all the answers

Which of the following statements about electric fuses is true?

Fuses provide protection against excess current by melting. Signup and view all the answers

What is the primary purpose of the filament in an electric bulb?

To emit light and heat when current flows through it. Signup and view all the answers

Study Notes

Units of Resistance

Resistance is measured in ohms (Ω); defined as the resistance when a current of 1 ampere flows through a conductor with a potential difference of 1 volt.

Factors Affecting Resistance of a Conductor

Thick conducting wires reduce resistance in circuits, easily facilitating the flow of electric charge.
Resistance opposes electric charge flow, causing energy loss that needs minimization.

Key Factors Influencing Resistance

Length of the conductor: Resistance increases with the length.
Cross-sectional area: Resistance decreases with an increase in cross-sectional area; thicker wires have lower resistance.
Temperature: Higher temperatures generally lead to increased resistance, except for certain alloys.
Nature of the material: Different materials have unique resistivity characteristics; for example, metals typically have lower resistance than non-metals.

Relationship between Resistance and Dimensions

Resistance (R) is directly proportional to the length (l) of the conductor: R ∝ l.
Resistance is inversely proportional to the cross-sectional area (A): R ∝ 1/A.
Conductors’ circular cross-section leads to area relation: A ∝ r² (radius).

Resistivity

Defined as the resistance of a material with unit length and unit cross-sectional area; measured in ohm-meters (Ω·m).
Resistivity varies with temperature and is a material-specific property.

Conductivity

Reciprocal of resistivity; measured in siemens per meter (S/m) or ohm⁻¹·m⁻¹.

Devices for Resistance Management

Rheostat: A variable resistor that adjusts resistance by varying the length of its wire.
Resistance Box: Contains multiple resistors in series for adjustable resistance based on circuit needs.

Temperature Dependency

Resistance typically increases with temperature; alloys (e.g., nichrome) show less sensitivity to temperature changes.

Semiconductors

Materials like germanium and silicon have electrical properties between conductors and insulators; resistivity decreases with rising temperature.

Electric Power

Defined as the rate of energy consumption: P = VI, where P is power, V is voltage, and I is current.
Measured in watts (W).
1 kilowatt (kW) = 1000 watts.
1 kilowatt-hour (kWh) represents energy consumption; 1 unit of energy is equal to 1 kWh.

Electric Appliances Calculation

Common household appliances have specified wattages; current drawn can be calculated via P = VI.

Heating Effect of Current

Electrical devices (e.g., room heaters) convert electrical energy into heat.
The heating effect is significant in high-resistance materials (e.g., nichrome wires).

Joule’s Heating

Energy from current flowing through resistance dissipates as heat, increasing wire temperature.

Electric Bulb

Edison's invention utilized high-melting-point filaments for better longevity; tungsten is commonly used today for its heat resistance.

Electric Fuse

A low-melting point device used for circuit protection to prevent damage from excess current by breaking the circuit once the current rises above safe levels.

Power Transmission

Generated electricity is transmitted via transformers, wires, and towers for industrial and household use, ensuring efficient distribution.

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Description

This quiz explores the concepts of resistance in electrical conductors, including its unit of measurement (ohms) and the factors affecting resistance. Test your understanding of why thicker wires are recommended for wiring and how resistance impacts circuit behavior.