Resistance

To determine the correct units for specific resistance, let's analyze the concept step by step.

1. Understanding Specific Resistance:
Specific resistance (also known as resistivity) is a material property that quantifies how strongly a material opposes the flow of electric current. It is denoted by the symbol (rho).

The formula for resistivity is given by:
$ R \Omega A m^2 L m \rho = \frac{R \cdot A}{L} R \Omega A m^2 L m \rho {(A) \, \Omega \cdot m} $

To solve the problem, we need to find the unknown resistance when three resistors are connected in series and the total resistance is given.

1. Understanding Series Connection:
In a series connection, the total or resultant resistance is the sum of all individual resistances:

2. Substitute the Known Values:
Given: , , and
Also,

3. Solve for R:

Final Answer:
The correct answer is option (D): 8 Ω.

To solve the problem, we need to find the resistance of the bulb given its power and voltage.

1. Use the Power Formula:
The power of an electrical device is related to voltage and resistance by the formula:
where is the power in watts, is the voltage in volts, and is the resistance in ohms.

2. Rearranging the Formula to Solve for Resistance:
Rearranging the formula to find resistance:

3. Substituting the Given Values:
Given and , substitute these values into the formula:

Final Answer:
The resistance of the bulb is .

To solve the problem, we need to understand how the resistance of a wire is affected by changes in its cross-sectional area, while keeping its temperature and length constant.

1. Formula for Resistance:
The resistance of a wire is given by the formula:



Where:
= resistivity of the material (constant for a given material)
= length of the wire
= area of cross-section

2. Given Conditions:
- Temperature is constant
- Length is constant
- Area increases

3. Analyzing the Relationship:
From the formula, resistance is inversely proportional to area :



So, if the area increases, the resistance decreases.

Final Answer:
The resistance of the wire when the area of cross-section increases.