type: misconceptions | topic: all-experiments
| # | Misconception | Correction |
|---|---|---|
| 1 | "Positive zero error should be added to get correct reading." | WRONG. Positive zero error means instrument reads MORE → SUBTRACT. "Positive → Subtract." |
| 2 | "v = 4fl_{1} and v = 2f(l_{2}−l_{1}) give the same answer." | WRONG. v = 4fl_{1} includes end correction (reads 4f(l_{1}+e)), while v = 2f(l_{2}−l_{1}) eliminates it. |
| 3 | "The vs l graph for a simple pendulum passes through (0, some positive value)." | WRONG. = (4π^{2}/g)l → graph passes through origin (no y-intercept). If it does not, there is a systematic error. |
| 4 | "A higher LC means higher precision." | WRONG. Higher precision means SMALLER LC (LC = 0.01 mm is more precise than LC = 0.02 mm). |
| 5 | "For a concave mirror, the focal length is positive." | WRONG. In Cartesian convention, concave mirror f < 0 (negative). Convex mirror f > 0 (positive). |
| 6 | "The lens formula and mirror formula are the same." | WRONG. Mirror: 1/v + 1/u = 1/f. Lens: 1/v − 1/u = 1/f. The sign before 1/u differs. |
| 7 | "Si and Ge diodes have the same threshold voltage." | WRONG. Si: ~0.7V; Ge: ~0.3V. Different band gaps cause different thresholds. |
| 8 | "A Zener diode can be used without a series resistor safely." | WRONG. Without R_series, current is unlimited → diode overheats and burns. Always use a series resistor. |
| 9 | "The balance length in a metre bridge is measured from end B." | WRONG. l is conventionally measured from end A (where the known resistance R is connected). l' = 100−l after interchange. |
| 10 | "Apparent depth > real depth when looking through a denser medium." | WRONG. Apparent depth < real depth. μ = real/apparent → apparent = real/μ < real (since μ > 1). |