What is the current required to light a 60 W incandescent bulb in a domestic supply of 240 V?
- A.0.5 A
- B.0.25 A
- C.1.0 A
- D.5.0 A
Correct answer
Explanation
The correct answer is B, 0.25 A. Electric power equals voltage times current, so the current is 60 W ÷ 240 V = 0.25 A.
The relation P = VI comes straight from the definitions: voltage is energy per unit charge and current is charge per second, so their product is energy per second, or power. The same bulb has a resistance of V²/P = 240² ÷ 60 = 960 Ω when hot. Knowing the current also helps choose a fuse: a circuit carrying several such bulbs needs a fuse rated a little above their total current.
A, 0.5 A, would mean a power of 240 × 0.5 = 120 W, twice the bulb's rating.
C, 1.0 A, would mean 240 W, four times the rating.
D, 5.0 A, would mean 1200 W, the kind of load drawn by a heater or an iron, not a bulb.
Exam tip: I = P/V and R = V²/P; a bulb's wattage at its rated voltage gives both at once.
Practice Questions
View allRecently, there was a growing awareness in our country about the importance of Himalayan nettle (Girardinia diversifolia) because it is found to be a sustainable source of
- A.anti-malarial drug
- B.biodiesel
- C.pulp for paper industry
- D.textile fibre
Show answer
The Himalayan nettle yields a strong natural fibre that can be spun and woven into cloth. Girardinia diversifolia, known as Himalayan giant nettle or allo, is a stinging shrub that grows wild in the moist forests of the Himalayas, including Uttarakhand, Himachal Pradesh and the North-east, as well as Nepal.
Read the full explanation →Which of the following statements are correct regarding the general difference between plant and animal cells ? 1. Plant cells have cellulose cell walls whilst animal cells do not. 2. Plant cells do not have plasma membrane unlike animal cells which do. 3. Mature plant cell has one large vacuole whilst animal cell has many small vacuoles. Select the correct answer using the code given below:
- A.1 and 2 only
- B.2 and 3 only
- C.1 and 3 only
- D.1,2 and 3
Show answer
Plant cells have a cellulose wall and one large central vacuole, but they do have a plasma membrane, just like animal cells.
Read the full explanation →Consider the following statements : 1. In tropical regions, Zika virus disease is transmitted by the same mosquito that transmits dengue. 2. Sexual transmission of Zika virus disease is possible. Which of the statements given above is/are correct ?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Show answer
Zika is spread mainly by the Aedes mosquito that also carries dengue, and it can pass between sexual partners. The Zika virus is a flavivirus first identified in Uganda's Zika forest in 1947.
Read the full explanation →What is the importance of using Pneumococcal Conjugate Vaccines in India ? 1. These vaccines are effective against pneumonia as well as meningitis and sepsis. 2. Dependence on antibiotics that are not effective against drug-resistant bacteria can be reduced. 3. These vaccines have no side effects and cause no allergic reactions. Select the correct answer using the code given below :
- A.1 only
- B.1 and 2 only
- C.3 only
- D.1, 2 and 3
Show answer
The vaccine protects against several pneumococcal diseases and so cuts antibiotic use, but no vaccine is free of side effects.
Read the full explanation →Which one of the following is NOT true for bleaching powder?
- A.It is used as a reducing agent in chemical industries
- B.It is used for bleaching wood pulp in paper factories
- C.It is used for disinfecting drinking water
- D.It is used for bleaching linen in textile industry
Show answer
Bleaching powder is an oxidising agent, not a reducing agent, so this statement is the false one. Bleaching powder, calcium oxychloride (CaOCl₂), is made by passing chlorine gas over dry slaked lime, Ca(OH)₂.
Read the full explanation →