Physics: Mechanics, Optics, Electricity and Modern Physics
The Physics section of the AIIMS B.Sc. Nursing entrance exam tests 10+2-level mechanics, heat, optics, electricity and modern physics. Most questions are single-step numericals or conceptual one-liners, so formula recall plus correct units matters more than long derivations.
Core rules and concepts
- Units and dimensions: convert every quantity to SI before substituting; check dimensional consistency to catch errors.
- Vectors: resolve into perpendicular components; the horizontal component of projectile velocity stays constant while the vertical component changes at g.
- Optics sign convention (Cartesian): measure all distances from the pole or lens centre, with the incident-light direction positive. Focal length of a convex lens is positive, concave negative.
- Electricity: Ohm's law V = IR; series adds resistance, parallel adds conductance; power P = VI = I²R = V²/R.
- Modern physics: photoelectric equation hν = φ + KE_max; photon energy E = hc/λ.
Worked example
A convex lens of focal length 10 cm forms an image of an object placed 15 cm away. Using 1/v − 1/u = 1/f with u = −15 cm and f = +10 cm: 1/v = 1/10 + 1/(−15) = 1/30, so v = +30 cm. Magnification m = v/u = 30/(−15) = −2. The image is real, inverted and twice the object size. The positive v confirms it lies on the opposite side, as expected for a real image.
Traps that cost marks
- Forgetting to convert cm to m or g to kg in numericals.
- Using v/u for mirrors - mirror magnification is −v/u.
- Confusing rms and peak values: V_rms = V_peak/√2 for a sine wave.
- Treating mass and weight as identical, or ignoring that g varies with altitude.