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- Question
A copper wire of radius r and length lhas a resistance of R. A second copper wire with radius 2r and length lis taken and the two wires are joined in a parallel combination. The resultant resistance of the parallel combination of the two wires will be
Options- A. 5 R
- B. 5 R/4
- C. 4 R/5
- D. R/5
- Correct Answer
- R/5
Explanation1st copper wire: R = pl/A = pl/ ?r2
2ndcopper wire: R? = p?l?/A? = pl/(4 ?r2) = R/4
If joined in parallel, (1/Req) = (1/R) + (1/R?)
= 1/R + 4/R1/Req= 5/R
Req= R/5
- 1. Consider the electromagnetic radiations having wavelengths 200 nm, 500 nm and 1000 nm. Which wavelength (s) of the following can make visual sensation to a human eye?
Options- A. 200 nm and 500 nm
- B. 500 nm and 1000 nm
- C. 500 nm only
- D. 200 nm and 1000 nm Discuss
- 2. Soap bubble attains spherical shape due to ______.
Options- A. inertia
- B. pressure
- C. surface tension
- D. Viscosity Discuss
- 3. If objects appear enlarged and inverted in a rear view mirror, then which type of mirror is used?
Options- A. Concave
- B. Convex
- C. Cylindrical
- D. Plane Discuss
- 4. What is the SI unit of electric current?
Options- A. Newton
- B. Joule
- C. Ampere
- D. Watt Discuss
- 5. What is the SI unit of frequency?
Options- A. Newton
- B. Watt
- C. Farad
- D. Hertz Discuss
- 6. The optical phenomenon that is primarily responsible for the observation of rainbow on a rainy day is
Options- A. diffraction
- B. interference
- C. dispersion
- D. reflection Discuss
- 7. Electric Motor converts _____ energy to mechanical energy
Options- A. sound
- B. mechanical
- C. chemical
- D. electrical Discuss
- 8. What is the SI unit of intensity of sound?
Options- A. Decible
- B. Newton
- C. Heartz
- D. Tesla Discuss
- 9. When a ball is thrown vertically upwards, which of the following quantities remains constant during its motion?
Options- A. Energy
- B. Displacement
- C. Velocity
- D. Acceleration Discuss
- 10. A ball rolling along the ground gradually slows down and finally comes to rest is due to ________.
Options- A. Friction
- B. Magnetic force
- C. Electrostatic force
- D. Muscular force Discuss
Physics problems
Search Results
Correct Answer: 500 nm only
Explanation:
Visual image of human eye is 390-700 nanometer. So, approximate value is 500 nanometer only.
Correct Answer: surface tension
Correct Answer: Concave
Correct Answer: Ampere
Correct Answer: Hertz
Correct Answer: dispersion
Explanation:
A rainbow is a natural spectrum appearing in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrops.
Correct Answer: electrical
Correct Answer: Decible
Correct Answer: Energy
Correct Answer: Friction
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