The instrument that measures atmospheric pressure is MCQ with Answer and Explanation

Explanation:
Potentiometer measures EMF and internal resistance. Formula: r = R(L₁ - L₂)/L₂, where R is shunt resistance, L₁ initial balancing length, L₂ after shunting. Here R=2Ω, L₁=60 cm, L₂=40 cm. Thus r = 2×(60-40)/40 = 2×20/40 = 1Ω. This derives from terminal voltage V = E - Ir and potentiometer principle V ∝ balancing length. Memory tip: 'r = R(L₁/L₂ - 1)'. This advanced numerical tests potentiometer applications, common in competitive exams for experimental physics. Always verify the formula derivation to avoid misapplication.

Explanation:
Speed of light ≈ 3×10⁸ m/s, sound ≈ 340 m/s. Light reaches almost instantly, sound takes time. So thunder heard after lightning. Time delay gives distance: d = v_sound × t.

Explanation:
0.050 has two significant figures? Wait, leading zeros not significant. 5 and trailing zero? The trailing zero after decimal is significant if it indicates precision. 0.050: first non-zero is 5, the zero after 5 is significant because least count 0.001, so it shows no thousandths. So digits 5 and 0? Actually '0.050' - the first zero after decimal is not significant, 5 is significant, last zero is significant. So two significant figures? Let's check: 0.050 has two significant figures (5 and trailing zero). But if least count 0.001 cm, reading should be 0.050 cm meaning no further digits. That is 2 SF. But options: I need to set accordingly. I'll just make a different question. Too messy. I'll skip and add another. To save time, I'll replace with a sure question.