Physics Sessional Viva Prep

phy-1109 PHY-1109 Physics

1. Fundamental Measurements and Error Analysis (Exp 0)

Experiment	Process Description	Key Data Taken	Key Formulae
Instrumental Errors & Measurement	This experiment involved determining instrumental errors and measuring length, mass, and time. Slide Calipers were used to measure the diameter (and thus radius) of a pen. A Spherometer was used to measure the height of a lens. A Screw Gauge was also used to measure the diameter of a pen. A Stop-Watch was used to measure the time period of oscillation.	Main Scale Reading (M.S.R.), Vernier Scale Reading (V.S.R.) or Circular Scale Division (C.S.D.), Instrumental Error ($N$) (e.g., $-0.02\text{ mm}$ for screw gauge). Time in seconds for a specific number of vibrations.	Least Count (L.C.) = $\frac{\text{Pitch}}{\text{No. of divisions in the circular scale}}$. Total Reading ($D$) $=M.S.R.+V.S.R.\times V.C.\pm N$. Mean Time Period ($\bar{T}$) = $\frac{\text{Total Time}}{\text{No. of Vibrations}}$.

2. Thermal Properties

Experiment	Process Description	Key Data Taken	Key Formulae
Thermal Conductivity (Lees & Charlton)	The objective was to find the thermal conductivity ($K$) of a bad conductor slab ($S$). Steam was passed through a chamber ($C$) placed on the slab ($S$), which rested on a metal disc ($A$). Steady-state temperatures ${\theta }_1$ (upper disc) and ${\theta }_2$ (lower disc $A$) were recorded. Then, disc $A$ was heated and allowed to cool, and its temperature was noted at regular time intervals (e.g., half-minute intervals). A temperature vs. time graph was plotted to find the rate of cooling ($\frac{d\theta }{dt}$) at temperature ${\theta }_2$.	Diameter and Thickness ($d$) of the slab $S$. Steady temperatures ${\theta }_1$ and ${\theta }_2$. Time and Temperature data during the cooling of disc $A$. Mass ($M$) and specific heat ($S$) of the disc $A$.	$\mathbf{K}=\frac{MS}{A({\theta }_1-{\theta }_2)}\times \frac{d\theta }{dt}\times d$. (Where ${\theta }_1$ and ${\theta }_2$ are steady state temperatures, $M$ is mass, $S$ is specific heat, $A$ is area, $d$ is thickness, and $\frac{d\theta }{dt}$ is the rate of cooling at ${\theta }_2$).
Specific Heat of Liquid (Cooling Method)	The experiment uses Newton’s Law of Cooling, where the rate of heat loss is proportional to the temperature difference between the liquid and surroundings. Equal volumes of the liquid (e.g., kerosene) and water were successively heated and poured into the same calorimeter. The time taken ($t_1$ for water, $t_2$ for liquid) for the liquid to cool through the same temperature range (e.g., $70^{\circ }\text{C}$ to $45^{\circ }\text{C}$) was measured.	Time vs. Temperature readings for water cooling (to find $t_1$). Time vs. Temperature readings for kerosene cooling (to find $t_2$). Mass of water ($M_W$), mass of liquid ($M_1$), mass of calorimeter ($M_c$).	${\mathbf{S}}_1=\frac{M_W{S}_W{t}_2+M_c{S}_c(t_2-t_1)}{M_1{t}_1}$. (Where $S_W$ is the specific heat of water, $S_c$ is the specific heat of the calorimeter material, and $S_1$ is the specific heat of the liquid).

3. Wave Optics (Wavelength, Diffraction, Interference)

Experiment	Process Description	Key Data Taken	Key Formulae
Wavelength of Sodium Light (Grating)	A spectrometer was used to measure the angular deviation of light diffracted by a plane diffraction grating. The grating was set normal to the incident sodium light. The angle of diffraction ($\theta$) was measured by taking readings for the $n^{\text{th}}$ order spectra on the left and right sides of the direct image.	Vernier Constant of the spectrometer. Number of lines per cm on the grating ($N$). Main scale and Vernier readings for the left image and right image to determine $2\theta$ and mean $\theta$ for the $n=1$ and $n=2$ orders.	Wavelength ($\lambda$) $=\frac{\sin \theta }{nN}$. (Where $n$ is the order of the spectrum and $N$ is the number of lines per cm).
Wavelengths of Various Spectral Lines	This experiment was similar to the Sodium Light experiment but used a discharge tube (e.g., Helium, Neon, Argon) as the source, which produces multiple spectral lines. The angle of diffraction ($\theta$) was measured for each distinct color (red, orange, yellow, green, bluish green) in the 1st order spectrum ($n=1$).	Number of lines per cm on the grating ($N$). Main scale and Vernier readings for the left and right images for each spectral line/color to find the angle of diffraction $\theta$.	$\lambda =\frac{\sin \theta }{nN}$.
Wavelength by Newton’s Rings	Monochromatic sodium light was passed through a system containing a plano-convex lens on a plane glass plate, creating a thin air film. The resulting circular interference fringes (Newton’s rings) were observed with a traveling microscope. The diameter ($D_n$) of several dark/bright rings was measured by aligning the cross-wires to the left and right edges of the rings.	Diameter of the $n^{\text{th}}$ ring ($D_n$) and the $(n+m{)}^{\text{th}}$ ring ($D_{n+m}$). Radius of curvature of the lens ($R$).	$\lambda =\frac{(D_{n+m}{)}^2-D_n^2}{4mR}$. (Calculation involved plotting $D^2$ versus $n$ to find the slope, where $\lambda =\frac{1}{4R}\times \text{slope}$).

4. Electricity and Magnetism

Experiment	Process Description	Key Data Taken	Key Formulae
Resistance (Post Office Box)	The P.O. Box uses the principle of the Wheatstone Bridge ($\frac{P}{Q}=\frac{R}{S}$). Part 1: Determine an unknown resistance ($S$) by adjusting the ratio arms ($P,Q$) and the resistance arm ($R$) until the galvanometer shows no deflection (null point). Part 2: Measure resistances $R_1$ and $R_2$ separately, and then measure their equivalent resistance when connected in series ($R_S$) and in parallel ($R_P$) to verify the laws of combination.	Resistances $P$, $Q$, and $R$ that yield the null point for unknown resistance $R_1$, $R_2$, $R_S$, and $R_P$.	Unknown Resistance ($\mathbf{S}$) $=R\left(\frac{Q}{P}\right)$. Series Verification: $R_S=R_1+R_2$. Parallel Verification: $\frac{1}{R_P}=\frac{1}{R_1}+\frac{1}{R_2}$.
EMF Comparison (Potentiometer)	The experiment compared the electromotive forces ($E_1$ and $E_2$) of two cells. The cells were alternately connected to the galvanometer circuit. The jockey was moved along the potentiometer wire until the galvanometer showed zero deflection. This balance point length ($L_1$ for $E_1$, $L_2$ for $E_2$) was recorded. The rheostat resistance was adjusted, and the lengths were recorded again for repeatability.	Total length of the potentiometer wire (wire number and scale reading) corresponding to the null point $L_1$ and $L_2$ for $C_1$ and $C_2$, respectively.	EMF Ratio $=\frac{E_1}{E_2}=\frac{L_1}{L_2}$.

5. Modern Physics & Waves

Experiment	Process Description	Key Data Taken	Key Formulae
Planck’s Constant & Work Function	This experiment studied the photoelectric effect by finding the stopping potential ($V$) required to halt the flow of electrons from a photocell for light of different frequencies ($\nu$). Light from a source was passed through various colored filters (different $\lambda$). For each filter, a reverse (backing) voltage ($V$) was increased until the photo-current was exactly zero. A graph of stopping potential ($V$) versus frequency ($\nu$) was plotted.	Applied wavelength ($\lambda$), calculated frequency ($\nu$). Average backing voltage ($V$) (stopping potential) for each frequency. Slope and y-intercept of the $V$ vs. $\nu$ graph.	Photoelectric Equation: $E_K=h\nu -\omega$ or $eV=h\nu -\omega$. Stopping Potential Relationship: $V=\left(\frac{h}{e}\right)\nu -\frac{\omega }{e}$. Planck’s Constant ($\mathbf{h}$) $=\text{Slope}\times e$. Work Function ($\omega$) $=\text{Intercept of y-axis}\times e$.
Frequency of Tuning Fork (Melde’s)	A string was attached to a tuning fork and weighted via a pulley, setting it into stationary wave vibration. The frequency of the fork ($N$) was calculated by observing the number of well-defined loops ($p$) formed in the thread for a given tension ($T$). Measurements were taken in two modes: longitudinal (fork vibration parallel to string) and transverse (fork vibration perpendicular to string).	Tension ($T$) derived from the load placed on the pan. Number of loops ($p$). Total length of the thread ($L$) and mass per unit length ($m$).	Transverse Position: $N=\frac{1}{2l}\sqrt{\frac{T}{m}}$. Longitudinal Position: $N=2\times \frac{1}{2l}\sqrt{\frac{T}{m}}$. (Where $l$ is the length of one loop).