Ray Optics — MHT-CET Physics

Formulas (1)

• The Mirror Formula and Plane Mirrors · Mirror formula
  $$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}, \qquad m = -\frac{v}{u}$$

Watch out for (1)

• Thinking a half-covered mirror forms half an image
  → The Mirror Formula and Plane Mirrors

Formulas (3)

• Snell's Law and the Refractive Index · Snell's law
  $$\sin i = \mu\sin r, \qquad \mu = \frac{c}{v}$$
• Apparent Depth and Normal Shift · Apparent depth
  $$d_{\text{app}} = \frac{d}{\mu}, \qquad \text{shift} = d\left(1 - \frac{1}{\mu}\right)$$
• Total Internal Reflection · Critical angle
  $$\sin C = \frac{1}{\mu}, \qquad r_{\text{disc}} = \frac{h}{\sqrt{\mu^2 - 1}}$$

Watch out for (4)

• Taking μ as the fraction of speed kept
  → Snell's Law and the Refractive Index
• Multiplying by μ instead of dividing
  → Apparent Depth and Normal Shift
• Allowing total internal reflection from rarer to denser
  → Total Internal Reflection
• Giving red the smaller critical angle
  → Total Internal Reflection

Formulas (2)

• Deviation and Minimum Deviation · Prism
  $$\mu = \frac{\sin\frac{A + \delta_m}{2}}{\sin\frac{A}{2}}, \qquad \delta_{\text{thin}} = (\mu - 1)A$$
• Dispersion, Dispersive Power and Achromatism · Dispersive power
  $$\omega = \frac{\delta_V - \delta_R}{\delta_Y}, \qquad \omega_1P_1 + \omega_2P_2 = 0$$

Watch out for (3)

• Using the glass's own index in water
  → Deviation and Minimum Deviation
• Forgetting that a retracing ray meets the silvered face normally
  → Deviation and Minimum Deviation
• Dividing by the violet or red deviation
  → Dispersion, Dispersive Power and Achromatism

Formulas (2)

• The Lens Formula and Magnification · Lens formula
  $$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}, \qquad m = \frac{v}{u}$$
• Lensmaker's Equation and Combining Lenses · Lensmaker and combinations
  $$\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right), \qquad P = P_1 + P_2 - dP_1P_2$$

Watch out for (3)

• Taking v = nu for a real image in a lens
  → The Lens Formula and Magnification
• Adding focal lengths instead of powers
  → Lensmaker's Equation and Combining Lenses
• Using centimetres in the power
  → Lensmaker's Equation and Combining Lenses

Formulas (1)

• Magnifying Power and Resolution · Magnifying power
  $$M_{\text{micro}} = \frac{v_0}{u_0}\cdot\frac{D}{f_e}, \qquad M_{\text{tele}} = \frac{f_0}{f_e}$$

Watch out for (2)

• Thinking a large aperture raises the magnification
  → Magnifying Power and Resolution
• Using the full tube length as the objective's image distance
  → Magnifying Power and Resolution