GK: Class 12 General Q&A · Page 129
3,658 free answers on GK (General) for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
How to calculate normal weight in kg?
To calculate normal weight, use the Body Mass Index (BMI) formula: BMI = weight (kg) ÷ height² (m²). A healthy BMI range is 18.5-24.9. Multiply your height in meters suared by 18.5 and 24.9 to find your healthy weight range. For example, for 1.7m height: (1.7)² × 18.5 = 53.5 kg minimum; (1.7)² × 24.9 = 71.9 kg maximum.
- GeneralClass 12All
What is the weight formula?
The weight formula is Weight (W) = Mass (m) × Gravitational acceleration (g). On Earth, this is typically calculated as W = m × 9.8 m/s². Weight is measured in newtons (N) in the SI system, though in everyday use, we often express weight in kilograms or pounds. For example, a 70 kg person has a weight of approximately 686 newtons on Earth.
- GeneralClass 12All
What are the 3 Ohm's law formulas?
The three forms of Ohm's Law are: V = IR (Voltage euals current times resistance) Use to find voltage when you know current and resistance I = V/R (Current euals voltage divided by resistance) Use to find current when you know voltage and resistance R = V/I (Resistance euals voltage divided by current) Use to find resistance when you know voltage a
- GeneralClass 12All
What is a safe level of voltage?
Safe voltage levels depend on conditions, but general guidelines are: Extra-low voltage (ELV): Less than 50V AC or 120V DC (generally considered safe for direct contact) Low voltage: 50-1000V AC or 120-1500V DC (reuires precautions) Specific contexts: Dry conditions: Up to 50V AC generally safe Wet conditions: Even 12-24V can be dangerous Residential<
- GeneralClass 12All
What is the resistance of a 20 cm long wire?
To calculate the resistance of a 20 cm long wire, you need additional information: Reuired parameters: Material (determines resistivity, ρ) Cross-sectional area or diameter Formula: R = ρL/A Example: A 20 cm (0.2 m) copper wire with 1 mm² cross-sectional area has: R = (1.68 × 10⁻⁸ × 0.2)/(1 × 10⁻⁶) = 0.00336 Ω or 3.36 mΩ
- GeneralClass 12All
How to test electrical resistivity?
To test electrical resistivity: For Solid Materials: Prepare a sample of known dimensions Use a four-point probe or multimeter to measure resistance Apply formula: ρ = RA/L For Liuids: Use a conductivity cell with known cell constant Measure conductivity Calculate resistivity as reciprocal: ρ = 1/σ For Soil/Ground:
- GeneralClass 12All
What is resistivity and resistor?
Resistivity is a material property that uantifies how much a material opposes current flow, measured in Ω·m. Resistor is an electrical component designed to provide a specific amount of resistance in a circuit, measured in ohms (Ω). Think of it this way: resistivity describes the material (like copper or carbon), while a resistor is a manufactured device made from resistive materials to control current in electronic circuits
- GeneralClass 12All
What is the resistivity of 1 ohm?
This uestion contains a misconception. Resistivity is not measured in ohms—it's measured in ohm-meters (Ω·m). One ohm (1 Ω) is a unit of resistance, not resistivity. However, if you're asking about a material with 1 ohm of resistance: A 1-meter cube of material with 1 Ω resistance has resistivity of 1 Ω·m The actual resistivity depends on the object's dimensions using ρ = RA/L
- GeneralClass 12All
What is resistivity also called?
Resistivity is also called: Specific resistance: Emphasizes it's a material-specific property Electrical resistivity: Distinguishes it from thermal resistivity Volume resistivity: Distinguishes it from surface resistivity In scientific literature, it's commonly represented by the Greek letter rho (ρ).
- GeneralClass 12All
What happens when resistivity is high?
When resistivity is high: Current flow decreases for a given voltage (poor conductivity) Heat generation increases if current is forced through the material Material acts as an insulator, preventing unwanted current flow Energy loss occurs if used as a conductor Applications include: electrical insulation, protective barriers, resistive heating elements</
- GeneralClass 12All
How to calculate resistivity from sheet resistance?
Sheet resistance (Rs) applies to thin films and is measured in ohms per suare (Ω/□). To calculate resistivity: ρ = Rs × t Where: ρ = resistivity (Ω·m) Rs = sheet resistance (Ω/□) t = thickness of the film (m) Example: If a thin film has sheet resistance of 100 Ω/□ and thickness of 50 nm (5 × 10⁻⁸ m), then ρ = 100 × 5 × 10⁻⁸ = 5
- GeneralClass 12All
What is the Ohm's law of resistivity?
While Ohm's Law (V = IR) describes the relationship between voltage, current, and resistance, it can be expressed in terms of resistivity as: E = ρJ Where: E = electric field (V/m) ρ = resistivity (Ω·m) J = current density (A/m²) This is the microscopic form of Ohm's Law, showing that electric field is proportional to current density, with resistivity as the proportionality constant.<
- GeneralClass 12All
What is the main formula for resistance?
The main formula for resistance is Ohm's Law: R = V/I Where: R = resistance in ohms (Ω) V = voltage in volts (V) I = current in amperes (A) Another fundamental formula relates resistance to physical properties: R = ρL/A, connecting resistance to resistivity, length, and cross-sectional area.
- GeneralClass 12All
How do you find the resistivity of a wire?
To find the resistivity of a wire: Step 1: Measure the wire's resistance (R) using a multimeter Step 2: Measure the wire's length (L) with a ruler or measuring tape Step 3: Measure the wire's diameter (d) using calipers Step 4: Calculate cross-sectional area: A = π(d/2)² Step 5: Calculate resistivity: ρ = RA/L Example: A copper wire with R = 0.5 Ω, L = 10 m,
- GeneralClass 12All
What is 4 pin soil resistivity test?
The 4-pin soil resistivity test (Wenner method) measures ground resistivity for electrical grounding systems: Procedure: Four electrodes are driven into the ground in a straight line at eual spacing (distance 'a') Current is injected through the outer two electrodes Voltage is measured between the inner two electrodes Resistivity is calculated using: ρ = 2πaR, where R = V/I This test is crucial for de
- GeneralClass 12All
Which instrument is used to measure resistivity?
Several instruments measure resistivity: Four-point probe resistivity meter: Industry standard for semiconductors and thin films Earth/Ground resistance tester: Measures soil resistivity Megohmmeter (Megger): Measures high-resistance materials Digital multimeter with four-wire resistance: For precise measurements LCR meter: Measures resistance, inductance
- GeneralClass 12All
How is resistivity measured?
Resistivity is measured using several methods: Four-Point Probe Method (most common): Four eually spaced probes contact the material Current passes through outer two probes Voltage is measured between inner two probes Eliminates contact resistance errors Two-Point Method: Measures resistance directly using an ohmmeter Calculates resistivity using ρ = RA/L <
- GeneralClass 12All
What is the resistivity of a solution?
The resistivity of a solution depends on the concentration and type of dissolved ions. Ionic solutions are generally good conductors with low resistivity: Concentrated salt solution: 0.05-0.1 Ω·m Dilute electrolytes: 1-100 Ω·m Very dilute solutions: approaching that of pure water The more ions present, the lower the resistivity and the better the conductivity. This p
- GeneralClass 12All
What is the maximum resistivity of water?
The maximum resistivity of water is approximately 1.8 × 10⁷ Ω·m, achieved only with ultra-pure, deionized water under laboratory conditions. In practice, perfectly pure water (18.2 MΩ·cm or 1.82 × 10⁶ Ω·m) is considered the practical maximum, as even the slightest contamination or dissolved gases will lower this value.
- GeneralClass 12All
What is the resistivity of water?
The resistivity of water varies dramatically based on purity: Pure (distilled) water: approximately 2.5 × 10⁵ Ω·m (high resistivity, poor conductor) Tap water: approximately 20-200 Ω·m Seawater: approximately 0.2 Ω·m (low resistivity due to dissolved salts) Pure water is actually a poor conductor. It's the dissolved ions and minerals that make ordi