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Quizzes > Science > Physics

Conduction vs Convection vs Radiation: Take the Ultimate Heat Transfer Quiz

Ready to ace convection and conduction and radiation questions? Start the quiz now!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration showing conduction convection radiation elements on teal background for heat transfer quiz

This quiz helps you practice conduction vs convection vs radiation and learn to tell how heat moves by contact, currents, and waves. Get quick feedback to find gaps before a test, then keep going with our heat transfer practice or go deeper with a convection quiz.

Which mode of heat transfer requires direct contact between particles to transfer energy?
Convection
Conduction
Advection
Radiation
Conduction transfers heat through direct interactions between neighboring particles without bulk movement of the medium. In conduction, kinetic energy is passed from molecule to molecule via collisions and vibrations. This mode is most prominent in solids due to close molecular spacing.
Which heat transfer mechanism involves the bulk movement of fluid carrying thermal energy?
Advection
Convection
Radiation
Conduction
Convection occurs when heat is transferred by the movement of fluid mass, such as air or liquid, carrying energy with it. This phenomenon is driven by buoyancy forces in natural convection or by external means in forced convection. It is distinct from conduction, which relies on molecular interactions, and radiation, which uses electromagnetic waves.
Which heat transfer mode uses electromagnetic waves to transfer energy without requiring a physical medium?
Radiation
Conduction
Convection
Advection
Radiation transfers heat through electromagnetic waves, primarily infrared, and does not need a material medium. Objects emit and absorb radiant energy depending on their temperature and surface properties. Even in a vacuum, such as space, radiation can occur.
Which of the following is an example of conduction?
Feeling heat from the sun on your face
Warm air rising above a heater
A metal spoon warming up when its handle is held in hot water
Steam condensing on a cold surface
In this example, heat flows along the metal spoon from the hotter end immersed in water to the cooler handle by conduction through atomic interactions. There is no bulk fluid movement or electromagnetic radiation involved. The metal's high thermal conductivity facilitates the heat flow.
Which scenario best illustrates convective heat transfer?
A hot pan heating a cold countertop
Warm air rising from a radiator and circulating around a room
Heat from a light bulb warming your skin
Heat diffusing through a solid wall
Warm air rising and circulating around a room exemplifies convection, where fluid motion transports heat. Buoyancy-driven flows occur in natural convection without external fans. In contrast, conduction and radiation do not involve bulk fluid movement.
Which of these is an example of heat transfer by radiation?
Air currents distributing heat
Feeling warmth from a fireplace without touching it
Hot water circulating in pipes
Heat spreading along a metal rod
Feeling warmth from a fireplace without direct contact or fluid movement illustrates radiation, where electromagnetic waves carry energy through space. No medium is needed for this transfer. Conduction and convection involve particle collisions and fluid flow, respectively.
Which mode of heat transfer does not require a medium and can occur in a vacuum?
Radiation
Convection
Conduction
Evaporation
Radiation transmits heat via electromagnetic waves, which can propagate through a vacuum without particles. Conduction and convection need a material medium, and evaporation is a phase change process requiring a liquid. Hence, only radiation can transfer energy in space.
Which heat transfer mode is least dependent on the thermal conductivity of the material?
Conduction
Convection
Sublimation
Radiation
Radiation depends on surface properties, temperature, and emissivity, not on bulk thermal conductivity. Conduction and convection rates are strongly tied to how well materials conduct heat and fluid properties. Sublimation refers to a phase change, not a primary heat transfer mechanism.
Which change will increase the rate of heat conduction through a solid?
Adding an insulating layer
Reducing the thermal conductivity
Increasing the temperature difference across the material
Decreasing the cross-sectional area
The rate of heat conduction is directly proportional to the temperature gradient across a material, as described by Fourier's law. Increasing the difference raises the gradient, boosting heat transfer. Reducing area or adding insulation lowers conduction, and lowering conductivity hinders it.
A material with high thermal conductivity will primarily exhibit:
High thermal radiation
Low heat capacity
Strong convective currents
Rapid heat conduction
High thermal conductivity indicates that a material quickly transfers heat through conduction. It does not directly affect convection or radiation rates, which depend on fluid flow and surface properties. Thermal conductivity is separate from heat capacity.
Which class of materials relies on free electrons to facilitate thermal conduction?
Polymers
Ceramics
Metals
Gases
Metals have delocalized free electrons that efficiently carry thermal energy across the lattice, making them excellent conductors. In non-metals like ceramics and polymers, conduction is dominated by lattice vibrations (phonons). Gases conduct heat poorly compared to solids.
What differentiates natural convection from forced convection?
Natural convection is driven by buoyancy forces without external equipment
Natural convection does not involve fluid motion
Natural convection requires a pump or fan
Natural convection only occurs in solids
Natural convection arises from density differences in a fluid due to temperature gradients, causing flow without external mechanical devices. Forced convection uses fans or pumps to move the fluid. Both involve fluid motion, and neither occurs in solids.
What does the emissivity of a surface represent?
Its temperature relative to the surroundings
The ratio of its radiation emission to that of a blackbody at the same temperature
Its ability to conduct heat through conduction
The rate of convective heat transfer
Emissivity quantifies how effectively a real surface emits thermal radiation compared to an ideal blackbody at the same temperature, with values from 0 to 1. It does not measure conduction or convection and is independent of the actual temperature difference.
A perfect blackbody is defined as:
A perfect thermal conductor
A surface with zero temperature
A fluid with no viscosity
An ideal absorber and emitter of all incident radiation
A blackbody is an idealized object that absorbs all incident electromagnetic radiation and emits the maximum possible radiation at each wavelength, as described by Planck's law. It is unrelated to electrical conduction or fluid viscosity.
Which law states that the power radiated per unit area of a blackbody is proportional to the fourth power of its absolute temperature?
Fourier's law
Boyle's law
Stefan - Boltzmann law
Newton's law of cooling
The Stefan - Boltzmann law describes how a blackbody's radiative heat flux is proportional to T^4, where T is absolute temperature, and ? is the Stefan - Boltzmann constant. Fourier's law addresses conduction, Newton's law approximates convective cooling, and Boyle's law relates pressure and volume of gases.
When two layers of different materials conduct heat in series, the total thermal resistance equals:
The ratio of conductivities
The sum of individual resistances
The product of individual resistances
The difference between resistances
In series conduction, thermal resistances add like electrical resistances, R_total = R1 + R2 + …. This follows from steady-state Fourier conduction through layered media. Multiplying or subtracting resistances does not represent proper series addition.
Thermal contact resistance arises primarily from:
Microscopic roughness and air gaps between contacting surfaces
High thermal conductivity of materials
Bulk fluid convection
Radiation across gaps
Even polished surfaces have microscopic peaks and valleys that trap air at the interface, creating a resistance to heat flow - called contact resistance. High conductivity reduces bulk resistance but does not affect contact gaps. Convection and radiation refer to other modes, not the contacts between solids.
The Nusselt number is a dimensionless parameter defined as the ratio of:
Convective to conductive heat transfer
Radiative to conductive heat flux
Gravitational to inertial forces
Inertial to viscous forces
The Nusselt number (Nu) quantifies the enhancement of heat transfer through a fluid layer by convection compared to pure conduction across the same boundary. High Nu indicates effective convective transport. Other dimensionless numbers represent different force or energy ratios.
Which dimensionless number characterizes the onset of natural convection by comparing buoyancy to viscous forces?
Reynolds number
Prandtl number
Grashof number
Péclet number
The Grashof number (Gr) measures the ratio of buoyancy to viscous forces in a fluid, determining when natural convection will develop. Reynolds number compares inertial to viscous forces in forced flow. Prandtl number relates momentum to thermal diffusivity, and Péclet number combines Reynolds and Prandtl.
Which empirical correlation is commonly used to estimate the convective heat transfer coefficient in turbulent pipe flow?
Kirchhoff's law
Ohm's law
Planck's law
Dittus - Boelter equation
The Dittus - Boelter equation (Nu = 0.023 Re^0.8 Pr^n) is widely applied to calculate convective heat transfer coefficients in turbulent flow inside smooth pipes. It relates dimensionless parameters of the flow and fluid. Planck's and Kirchhoff's laws refer to radiation, and Ohm's law to electrical circuits.
In radiative heat exchange between two surfaces, the view factor represents:
The Stefan - Boltzmann constant
The thermal conductivity of the medium
The emissivity of the surface
The fraction of radiation leaving one surface that strikes the other
The view factor (or configuration factor) quantifies the portion of radiation energy leaving one surface that directly reaches another, considering geometry. It is crucial for calculating radiative heat transfer in enclosures. Emissivity, conductivity, and ? are separate properties.
What is the net radiative heat transfer between two infinite parallel plates with emissivities ?1 and ?2 at temperatures T1 and T2?
q = ?1?2?A(T1^3 ? T2^3)
q = hA(T1 ? T2)
q = ?A(T1^4 ? T2^4)/(1/?1 + 1/?2 ? 1)
q = kA(T1 ? T2)/L
For two infinite parallel plates exchanging radiation, the net heat flux is given by ?A(T1^4 ? T2^4) divided by (1/?1 + 1/?2 ? 1), accounting for emissivities. The other expressions denote convective or conductive formulas or incorrect radiative forms.
For fully developed laminar flow in a circular pipe with constant wall temperature, the Nusselt number is:
3.66
7.54
4.36
0.023Re^0.8Pr^0.4
In fully developed laminar flow in a pipe with constant surface temperature, the Nusselt number is a constant 3.66. This arises from analytical solutions of the energy equation. The other values or correlations apply to different conditions or turbulent flow.
What is the approximate critical Reynolds number at which flow in a circular pipe transitions from laminar to turbulent?
20000
2300
500
10000
The critical Reynolds number for transition in pipe flow is around 2300, below which flow is laminar and above which it becomes turbulent. This threshold can vary with disturbances but is a commonly accepted value.
In the Dittus - Boelter correlation for turbulent pipe flow, the exponent 'n' is typically set to ____ for heating of the fluid.
1.0
0.4
0.8
0.3
The Dittus - Boelter equation is Nu = 0.023 Re^0.8 Pr^n, where n = 0.4 for heating and n = 0.3 for cooling of the fluid. The exponent captures how Prandtl number influences heat transfer depending on flow direction.
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Study Outcomes

  1. Understand Heat Transfer Mechanisms -

    Identify and define conduction, convection, and radiation to build a solid foundation in thermal energy movement.

  2. Differentiate Conduction vs Convection vs Radiation -

    Compare each heat transfer method's unique characteristics, processes, and practical applications.

  3. Identify Examples of Convection and Conduction and Radiation -

    Recognize everyday scenarios that illustrate radiation convection and conduction to reinforce theoretical concepts.

  4. Analyze Molecular Collision in Direct Contact Heat Transfer -

    Examine how heat transfer through the collision of molecules - direct contact - drives conduction in solids and fluids.

  5. Apply Concepts to Fire Heat Transfer -

    Determine whether fire heat transfer is radiation or convection by evaluating real-world thermal dynamics.

Cheat Sheet

  1. Overview of Heat Transfer Mechanisms -

    In the study of conduction vs convection vs radiation, heat moves via three distinct pathways: direct molecular contact, fluid motion, and electromagnetic waves. Recognizing these modes on university sites like MIT's and NASA's resources helps you classify any heat flow scenario. Use the mnemonic "CCRa" (Conduction, Convection, Radiation always) to recall all three.

  2. Conduction: Molecular Collision -

    Conduction is heat transfer through the collision of molecules-direct contact, described by Fourier's Law (q = −kA·dT/dx), with k as thermal conductivity. You feel this when a metal spoon heats up in a hot soup - heat moves from hot molecules to cooler ones along the metal. Academic sources such as HyperPhysics emphasize that solids with high k (e.g., copper) conduct heat fastest.

  3. Convection: Fluid Motion -

    Convection and conduction and radiation differ because convection relies on bulk fluid movement, characterized by Newton's Law of Cooling (Q = hA·ΔT) and seen in both natural and forced forms. A classic example is boiling water: warmer fluid rises while cooler fluid sinks, creating convection currents. University lectures often highlight forced convection in HVAC systems versus natural convection in ocean currents.

  4. Radiation: Electromagnetic Waves -

    Radiation transfers energy via photons and doesn't require a medium - governed by the Stefan-Boltzmann Law (j* = εσT❴). You experience this when standing near a campfire: infrared radiation warms your skin even though thin air is a poor conductor. Examples of radiation convection and conduction include feeling sunlight (radiation), a heater fan (convection), and touching a hot pan (conduction).

  5. Comparing Modes & Real-World Application -

    To decide "is fire radiation or convection," note fire radiates intense IR waves while heated air rises to stir convection currents in a room. Fire's flavor of heat transfer often combines radiation for direct warmth and convection for ambient heating. This comparative view, supported by engineering handbooks, reinforces the unique roles of each mode in practical systems.

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