A typical LED converts electrical energy into light with efficiency around MCQ with Answer and Explanation

A typical LED converts electrical energy into light with efficiency around
A. 80-90%
B. 10%
C. 50-60%
D. 100%
Answer: Option A
Solution (By JKSSB Mock Tests)
LEDs are highly efficient, converting ~80-90% of electrical energy into light, rest heat. Incandescent bulbs ~10% efficient. LED long life, low power. Blue LED Nobel prize 2014.

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Practice More Physics Questions

Question #1
Photoelectric threshold frequency ν₀ = φ/h. If work function doubles, ν₀:
A. Doubles
B. Halves
C. Quadruples
D. Unchanged

Correct Answer: Option A


Explanation:
ν₀ ∝ φ. Double work function ⇒ double threshold frequency. Higher φ requires higher photon energy for emission. Memory tip: 'ν₀ = φ/h; larger φ ⇒ higher frequency needed'. Photoelectric effect relation frequently tested in competitive quantum physics sections.

This question belongs to: Science Physics
Question #2
A car starts from rest and accelerates uniformly at 2 m/s² for 10 s. Distance covered in 10th second is
A. 2 m
B. 10 m
C. 20 m
D. 19 m

Correct Answer: Option D


Explanation:
s_nth = u + (a/2)(2n-1) = 0 + (2/2)(20-1) = 19 m.

This question belongs to: Science Physics
Question #3
The device used for detecting and measuring small electric current is
A. Wattmeter
B. Voltmeter
C. Ammeter
D. Galvanometer

Correct Answer: Option D


Explanation:
Galvanometer is sensitive instrument for detecting presence and direction of small currents. Ammeter measures larger currents. Voltmeter potential difference. Wattmeter power.

This question belongs to: Science Physics