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Physics NEET MCQ
Quiz 1
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Q.1
A slab consists of two layers of different materials of the same thickness and having thermal conductivities. x and y are connected in series. The equivalent thermal conductivity of the slab is
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x+y
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$\sqrt {xy}$
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$\frac {xy}{x+y}$
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$\frac {2xy}{x+y}$
Explanation
For two slabs of EQUAL thickness d in series, the total thermal resistance adds: R_total = d/(xA) + d/(yA). Writing this as an equivalent single slab of thickness 2d: 2d/(k_eq·A) = (d/A)(1/x + 1/y) = (d/A)·(x+y)/(xy) 2/k_eq = (x+y)/(xy) → k_eq = 2xy/(x+y).
Q.2
A metal rod at a temperature of 150° C radiates energy at a rate of 20 W. if its temperature is increased to 300° C, then it will radiate at the rate of
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17.5 W
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37.2 W
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40.6 W
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68.3 W
Explanation
By Stefan's law, radiated power P ∝ T⁴ (T in kelvin). T₁ = 150+273 = 423 K, T₂ = 300+273 = 573 K. P₂/P₁ = (T₂/T₁)⁴ = (573/423)⁴ ≈ (1.355)⁴ ≈ 3.37 P₂ ≈ 20 × 3.37 ≈ 67–68 W.
Q.3
The Wien’s displacement law express the relation between
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wavelength corresponding to maximum energy and temperature
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radiation energy and wavelength
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temperature and wavelength
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colour of light and temperature
Explanation
Wien's displacement law states that the wavelength at which a black body emits the most energy (its peak wavelength) is inversely proportional to its absolute temperature — λ_max·T = constant.
Q.4
The latent heat of vaporisation of a substance is always
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greater than its latent heat of fusion
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greater than its latent heat of sublimation
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equal to its latent heat of sublimation
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less than its latent heat of fusion
Explanation
Converting a liquid fully into a gas (vaporisation) requires breaking essentially all the intermolecular attractions holding the liquid together, which takes more energy than the partial rearrangement needed just to melt a solid into a liquid (fusion) — so the latent heat of vaporisation is always greater than the latent heat of fusion for a given substance.
Q.5
A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is
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E/c
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2E/c
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Ec
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E/c2
Explanation
A photon carries momentum E/c. On perfect reflection at normal incidence, its momentum reverses direction entirely — so the change in the photon's momentum (and hence the momentum delivered to the surface) is E/c − (−E/c) = 2E/c.
Q.6
Steam at 100° C is passed into 1.1 kg of water contained in calorimeter of water equivalent 0.02 kg at 15 ° C till the temperature of the calorimeter rises to 80 ° C. What is the mass of steam condensed? Latent heat of stem =536 cal/g
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.065
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.195
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.130
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.260
Explanation
Heat gained by the water + calorimeter (15°C → 80°C): (1100 + 20) g × 1 cal/(g·°C) × (80−15) = 1120 × 65 = 72,800 cal Heat released by mass m (grams) of steam = latent heat of condensation + cooling from 100°C to 80°C: m × 536 + m × 1 × (100−80) = m × 556 Setting these equal: m = 72,800 / 556 ≈ 131 g ≈ 0.130 kg.
Q.7
An ideal black body at room temperature is thrown into a furnace. It is observed that
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Initially, it is the darkest body and at later times the brightest.
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It is the darkest body at all times.
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it cannot be distinguished at all times.
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Initially, it is darkest and at later times it cannot be distinguished.
Explanation
By Kirchhoff's law, a good absorber is also a good emitter. While the black body is still cool (just placed in the hot furnace), it absorbs essentially all incoming radiation and reflects none, making it look the darkest object around. Once it heats up to the furnace's temperature, being the best possible emitter too, it radiates the most strongly — appearing the brightest.
Q.8
Which of the following processes is reversible?
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Transfer of heat by conduction
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Transfer of heat by radiation
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Isothermal compression
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Electrical heating of a nichrome wire
Explanation
Isothermal compression, when carried out infinitely slowly (quasi-statically, staying in equilibrium at every step), is the classic example of a reversible thermodynamic process. Heat conduction and radiation always flow spontaneously from hot to cold and can't reverse on their own, and Joule (resistive) heating in a wire irreversibly dissipates electrical energy as heat.
Q.9
A bimetallic strip consists of metals X and Y. It is mounted rigidly at the base as shown. The Metal X has a higher coefficient of expansion compared to that for metal Y. When the bimetallic strip is placed in a cold bath
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it will bend towards the right
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it will bend towards the left
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it will not bend but shrink
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it will neither bend nor shrink.
Explanation
Metal X (higher expansion coefficient) contracts more than metal Y when cooled. Since X sits on the left side of the strip, its greater contraction pulls that side in more, making the strip curve — and its free end bend — towards the left (the side with more contraction becomes the concave/inner side of the bend).
Q.10
Two identical rods are connected between two containers one of them is at 100 ° C and another is at 0 °C. If rods are connected in parallel then the rate of melting of ice is a j/s. If they are connected in series then the rate is b. The ratio a/b is
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2 :1
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1: 2
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4: 1
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1: 4
Explanation
Let a single rod's heat-conduction rate (for the given temperature difference) be R. In parallel, two identical rods each carry their own full rate independently, so the combined rate a = 2R. In series, the rods act like one rod of double the length, halving the rate: b = R/2. a/b = 2R / (R/2) = 4, i.e. 4:1.
Q.11
In the following question, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given four responses and mark it as (a) If both assertion and reason are true and reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not correct explanation of the assertion. (c) If assertion is true, but reason is false. (d) If both assertion and reason are false. (e) If reason is true but assertion is false. Assertion: In a pressure cooker the water is brought to a boil. The cooker is then removed from the stove. Now on removing the lid of the pressure cooker, the water starts boiling against. Reason: The impurities in water bring down its boiling point
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a
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b
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c
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d
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e
Explanation
The Assertion is true: while sealed under a stove's heat, the water inside a pressure cooker gets hotter than 100°C because the trapped steam raises the internal pressure (and boiling point) above normal. The instant the lid is removed, pressure suddenly drops back to atmospheric, and the still-superheated water (above the new, lower boiling point) boils vigorously again. The Reason is false on its own terms too: dissolved impurities actually RAISE a liquid's boiling point (boiling-point elevation), they don't lower it — and in any case, it's the pressure change, not impurities, that causes the reboiling here.
Q.12
In the following questions, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given four responses and mark it as (a) If both assertion and reason are true and reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not correct explanation of the assertion. (c) If assertion is true, but reason is false. (d) If both assertion and reason are false. (e) If reason is true but assertion is false. Assertion: For higher temperatures the peak emission wavelength of a black body shifts to lower wavelengths. Reason: Peak emission wavelengths of a blackbody is proportional to the fourth power of temperature.
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a
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b
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c
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d
Explanation
The Assertion is correct (this is Wien's displacement law: λ_max ∝ 1/T, so hotter bodies peak at shorter wavelengths). But the Reason is false: Wien's law says the peak wavelength is inversely proportional to temperature (λ_max ∝ 1/T), not proportional to T⁴ — that fourth-power relationship instead describes total radiated POWER (Stefan-Boltzmann law), a completely different quantity. (The source data's marked option here treats the Reason as true, but it is factually incorrect as stated.)
Q.13
In the following questions, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given four responses and mark it as (a) If both assertion and reason are true and reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not correct explanation of the assertion. (c) If assertion is true, but reason is false. (d) If both assertion and reason are false. (e) If reason is true but assertion is false Assertion: Woolen clothes keep the body warm in winter Reason: Air is bad conductor of heat
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a
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b
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c
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d
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e
Explanation
Wool traps a layer of still air within its fibres, and since air is a poor conductor of heat, this trapped air layer forms an effective insulating barrier that slows heat loss from the body — which is exactly why woollen clothing keeps you warm.
Q.14
In the following questions, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given four responses and mark it as (a) If both assertion and reason are true and reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not correct explanation of the assertion. (c) If assertion is true, but reason is false. (d) If both assertion and reason are false. (e) If reason is true but assertion is false. Assertion: it is hotter over the top of fire than at the same distance on the sides. Reason: Air surrounding the fire conducts more heat upwards.
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a
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b
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c
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d
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e
Explanation
The Assertion is true: hot air rising by convection concentrates heat directly above a fire, making that region hotter than the sides at an equal distance. But the Reason is false — it's convection (bulk movement of heated, less dense air rising), not conduction, that carries heat upward here; in fact, air is generally a poor conductor of heat.
Q.15
Match the physical quantities given in List I to their dimensions in List II.
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P -> 4,Q -> 2,R ->1,S -> 3
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P -> 3,Q -> 2,R ->1,S -> 4
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P -> 4,Q -> 1,R ->2,S -> 3
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P -> 2,Q -> 3,R ->1,S -> 4
Explanation
Matching each quantity to its dimensional formula: (P) Boltzmann constant k: from E = kT, [k] = [Energy]/[Temperature] = ML²T⁻²K⁻¹ → (4) (Q) Coefficient of viscosity η: units N·s/m² = ML⁻¹T⁻¹ → (2) (R) Planck's constant h: from E = hν, [h] = [Energy]/[frequency] = ML²T⁻¹ → (1) (S) Thermal conductivity: from the heat-conduction equation, [k] = MLT⁻³K⁻¹ → (3) So: P → 4, Q → 2, R → 1, S → 3.
Q.16
Column I gives some devices and Column II gives some processes on which the functioning of these devices depend. Match the devices in Column I with the processes in Column II.
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A->p, B -> q, C -> s, D -> r
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A->s, B -> p, C -> q, D -> r
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A->r, B -> q ,C -> p, D -> s
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A->s, B -> q, C -> p, D -> r
Explanation
Matching each device to the process it relies on: (A) Bimetallic strip → thermal expansion of solids (different metals expand at different rates, causing bending) → (s) (B) Steam engine → energy conversion (heat energy into mechanical work) → (q) (C) Incandescent lamp → radiation from a hot body (a white-hot filament emitting light) → (p) (D) Electric fuse → melting (the fuse wire melts and breaks the circuit when current is excessive) → (r) So: A → s, B → q, C → p, D → r.
Q.17
The pressure of the gas in constant volume gas thermometer are 80 cm,90cm and 100cm of mercury at the ice point, the steam point and in a heated wax bath resp. Find the temperature of the wax bath
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150
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200
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180
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100
Explanation
Using the linear relation for a constant-volume gas thermometer, calibrated so that the ice point reads 0°C and the steam point reads 100°C: T = [(P − P_ice)/(P_steam − P_ice)] × 100 = [(100−80)/(90−80)] × 100 = (20/10) × 100 = 200°C.
Q.18
At a common temperature, a block of wood and a block of metal feel equally cool or hot. The temperatures of metal and wood are
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less than the temperature of the body
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equal to the temperature of the body
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greater than the temperature of the body
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either (a) or (c)
Explanation
Wood and metal only feel different from each other (one feeling colder or hotter than the other) when their temperature genuinely differs from the observer's body — differing thermal conductivities affect how quickly heat is exchanged when there IS a temperature gradient. If both feel neither hot nor cold ("equally cool or hot" as the body), that means no net heat is flowing either way, which only happens when their actual temperature equals the body's own temperature — regardless of what material they're made of.
Q.19
A sphere, a cube, and a disc all of the same material, quality, and volume are heated to 600 ºC and left in the air. Which of these will have the lowest rate of cooling?
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Sphere
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Cube
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Disc
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All will have the same rate
Explanation
For a fixed volume, cooling rate depends on surface area (more surface area radiates more heat per second). Among shapes of the same volume, a sphere has the smallest possible surface area — so it has the lowest rate of cooling of the three shapes.
Q.20
Mud houses are cooler in summer and warmer in winter because
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mud is a bad conductor of heat
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mud is a superconductor of heat
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mud is a good conductor of heat
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none of the above
Explanation
Mud is a poor (bad) conductor of heat, so a mud house resists heat flow between the hot/cold outside and the interior — keeping the inside cooler than the scorching outdoors in summer, and warmer than the cold outdoors in winter, by simply slowing down heat exchange in both directions.
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