Revision: Class 12 >> Experimental Skills NEET (UG) Experimental Skills

One metre is defined as the one ten-millionth part of distance from the pole to the equator.

One metre is defined as 1,650,763.73 times the wavelength of a specified orange-red spectral line in emission spectrum of Krypton = 86.
OR
One metre is defined as 1,553,164.1 times the wavelength of the red line in the emission spectrum of cadmium.

“The pitch of a screw is the distance moved by the screw in one complete rotation of its head.”
OR
Pitch may also be defined as “the distance between two consecutive threads of screw measured along the axis of the screw.”

Pitch = `"Distance moved by thimble on M.S."/"Number of rotations of thimble"`

Least count of a vernier callipers is the difference between one main scale division (M.S.D.) and one vernier scale division (V.S.D.)

The frequency with which a body oscillates freely is called natural frequency.

A simple pendulum whose period of oscillation is exactly two seconds is called a second’s pendulum.

An ideal simple pendulum consists a point mass suspended from a perfectly rigid support by weightless, inextensible and perfectly flexible fibre.

An ideal simple pendulum is a heavy particle suspended by a massless, inextensible, flexible string from a rigid support.

A heavy but small sized metallic bob suspended by a light, inextensible and flexible string, which performs oscillatory motion, is called a simple pendulum.

A simple pendulum whose period is two seconds is called a second's pendulum.

The viscous force acting per unit area between two layers of liquid moving with unit velocity gradient is called the coefficient of viscosity (η).

The amount of heat required to raise the temperature of one mole of a substance through a unit degree Celsius or Kelvin is called molar heat capacity.

The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of unit mass of that substance through 1°C (or 1 K).

OR

Heat capacity of a body when expressed for the unit mass is called the specific heat capacity of the substance of that body.

OR

The amount of heat energy required to raise the temperature of a unit mass of an object by 1 °C is called the specific heat of that object.

OR

The amount of heat per unit mass absorbed or given out by a substance to change its temperature by one unit (one degree), i.e., 1°C or 1 K, is called specific heat capacity.

OR

The quantity of heat required to raise the temperature of a unit mass of a gas by one degree, whose exact value depends upon the mode of heating the gas and can range from zero to infinity or even be negative, is called the specific heat capacity of a gas.

The heat capacity of a body is the quantity of heat required to raise its temperature by 1°C. It depends upon the mass and the nature of the body.

The quantity of heat needed to raise the temperature of the whole body by 1°C (or 1 K) is called heat capacity.

OR

The amount of heat ΔQΔQ supplied to a substance to change its temperature from T to T + ΔT, per unit mass per unit degree change in temperature, is called specific heat:

\[LC=\frac{\text{Smallest division on main scale}}{\text{Number of divisions on Vernier scale}}\]

\[\text{Actual Reading}=MSR+VSR\times LC\]

\[LC=\frac{\text{Pitch of screw}}{\text{Number of divisions on circular scale}}\]

\[\text{Actual Reading}=MSR+CSR\times LC\]

\[KE=\frac{1}{2}mv^2\]

\[PE=mgh\]

where,

m is mass

g is gravity

h is height

T = 2π\[\sqrt {\frac {l}{g}}\]

n = \[\frac {1}{2π}\]\[\sqrt {\frac {g}{l}}\]

T = 2π\[\sqrt{\frac {L_s}{g}}\] = 2 seconds

\[g=\frac{4\pi^2L}{T^2}\]

\[E=PE+KE\]

\[\text{Mass}=\frac{\text{Distance}_1}{\text{Distance}_2}\times\text{Known~mass}\]

\[Y=\frac{\text{Stress}}{\text{Strain}}\]

\[\sigma=\frac{F}{A}\]

\[\varepsilon=\frac{\Delta L}{L}\]

\[h=\frac{2T\cos\theta}{\rho gr}\]

Where,

T = surface tension

θ = contact angle

ρ = density

g = acceleration due to gravity

r = radius of the capillary tube in meter

\[W=T\times\Delta A\]

\[v_t=\frac{2r^2(\rho-\sigma)g}{9\eta}\]

Where,

r = radius of sphere

ρ = density of sphere

σ = density of liquid

η = coefficient of viscosity

\[v=2Lf\]

Where,

L = length of the resonance tube

f = frequency of the sound source

\[Q=mc\Delta T\]

Specific heat capacity c = \[\frac{\text{Heat capacity of body } C'}{\text{Mass of the body } m}\]

or

Specific heat capacity c = \[\frac{Q}{m\times\Delta t}\]

C = M × c = Q/(nΔT)

Unit: J/mol · K

\[R=\frac{R_2}{R_1}\times R_x\]

Where R₁, R₂, and Rₓ are resistances

\[\rho=\frac{RA}{l}\]

Where,

R = resistance

A = cross-sectional area

l = length of the wire

\[K=\frac{I}{\theta}\]

Where,

I = current through the galvanometer

θ =  deflection in divisions

Also written as:

\[K=\frac{V}{\theta}\]

\[R=\frac{V}{I}\]

\[f=\frac{d_1-d_2}{2}\]

Where,

f = focal length

d₁, d₂ = distances between the observer's eye and the optical device at two different head positions

\[\mu=\frac{(a_1-a_3)}{(a_1-a_2)}\]

Where,

a₁ = reading on mark without slab

a₂ = reading on mark with slab placed over it

a₃ = reading on the top surface of the glass slab

The viscous drag force on a spherical body moving through a viscous fluid is used to calculate the coefficient of viscosity. Terminal velocity is reached when the gravitational force equals the viscous drag force.

The voltage (V) across a conductor is equal to the product of the current (I) passing through it and its resistance (R):

\[V=IR\]

• A simple pendulum is a mass on a string swinging under gravity
• Used to determine acceleration due to gravity (g)
• Energy dissipation can be analysed by plotting the square of amplitude vs. time
• At any point: total mechanical energy = PE + KE
• PE depends on height; KE depends on velocity

• A metre scale uses the principle of moments to find the mass of an object.
• The object is balanced on a pivot point.
• Torques on both sides of the pivot are equated.
• Distance₁ = distance of unknown mass from pivot; Distance₂ = distance of known mass from pivot.
• Mass is calculated by the ratio of distances multiplied by the known mass.

• Surface tension arises due to cohesive forces between water molecules at the surface.
• Measured by the capillary rise method or by observing effects with/without detergents.
• Capillary rise depends on surface tension, contact angle, liquid density, and tube radius.
• Adding detergents reduces the surface tension of water.
• Surface energy = work done per unit increase in surface area.
• θ is the contact angle between the liquid and the tube wall.

• The speed of sound is measured using a resonance tube experiment.
• Resonance occurs when the air column length matches the sound wave.
• A tuning fork or sound source of known frequency is used.

• Heat energy absorbed (Q) depends on: mass (m), rise in temperature (Δt), and specific heat capacity (c), i.e., Q ∝ m × Δt × c.
• Heat capacity (C') and specific heat capacity (c) are related by: C′ = m × c.

• Resistivity is measured using a Wheatstone bridge or a meter bridge
• The meter bridge is a practical form of the Wheatstone bridge
• ρ depends on the material, not its shape or size
• R = resistance of wire; A = cross-sectional area; l = length of wire
• Wheatstone bridge formula is used to find the unknown resistance Rₓ
• Unit of resistivity is ohm-meter (Ω·m)

• The half deflection method determines both the resistance (G) and the figure of merit (K) of a galvanometer
• A known resistance R is connected in series with the galvanometer
• Potential difference V is applied until the galvanometer shows half of full-scale deflection
• Resistance of galvanometer G = 2R
• Figure of merit K = I ÷ θ (current per unit deflection)
• K indicates the sensitivity of the galvanometer

• The parallax method measures the focal length of convex mirrors, concave mirrors, and convex lenses
• The observer moves their head horizontally while observing the image
• The distance between the observer's eye and the optical device is measured at two different positions of the head
• The difference between the two distances is used to calculate the focal length
• For a convex mirror, focal length (f) = half the difference between the two measured distances
• No formula involving object/image distance (u, v) is used in this method

• When a ray of light passes through a triangular prism, it gets deviated due to refraction.
• The angle of deviation (δ) depends on the angle of incidence (i).
• The plot of δ vs i shows a non-linear relationship.
• Angle of deviation increases more rapidly at higher angles of incidence.
• The plot is used to determine the dispersion of light by prisms.
• It helps in finding the prism's refractive index.

• In forward bias, current increases exponentially with voltage due to the majority charge carrier flow.
• In reverse bias, the current is very small until the breakdown voltage is reached.
• The forward bias curve is used to determine forward voltage drop and forward resistance.
• The reverse bias curve is used to determine the reverse breakdown voltage.
• Breakdown voltage = voltage at which diode starts conducting in reverse direction.
• The characteristic curve has two distinct regions: forward bias and reverse bias.

• Diode allows current in one direction only; cathode identified by a colored band.
• LED emits light when current flows; it has a clear or colored lens.
• Resistor limits current; resistance value read via colour band code.
• A capacitor stores electrical energy temporarily.
• A capacitor is usually cylindrical or box-shaped with a value marked on it.
• All four components can be identified visually by their physical appearance.