All questions of Heat Transfer for JAMB Exam

Explanation:

The Geiger-Marsden experiment was conducted to study the structure of an atom. In this experiment, a beam of alpha particles was directed towards a thin gold foil. The alpha particles were expected to pass through the gold foil with little or no deflection, as it was believed that the positive charge and the negative electrons in an atom are distributed uniformly, reducing the electric field inside the atom. However, the results of the experiment were surprising, as some of the alpha particles were deflected at large angles, and some even bounced back.

Reasons for very small deflection of the beam:

- Electrical forces: According to Coulomb's law, any two charged particles exert a force on each other. In an atom, the positively charged nucleus and the negatively charged electrons are attracted to each other by electrical forces. However, the electrons are in constant motion, creating a cloud of negative charge around the nucleus. This cloud of negative charge reduces the electric field inside the atom, making it difficult for the alpha particles to be deflected.
- Distribution of charge: The positive charge in an atom is concentrated in the nucleus, while the negative charge is distributed throughout the atom. This distribution of charge makes the electric field inside the atom more uniform, reducing the chances of the alpha particles being deflected.
- Collimation of particles: The alpha particles were collimated by lead screens before they were directed towards the gold foil. This was done to ensure that the particles were traveling in a straight line and were not scattered by other particles or objects in the environment.
- Most particles pass through: Despite the above factors, it was still expected that some of the alpha particles would be deflected at small angles due to the random nature of the collisions between the particles and the atoms in the gold foil. However, it was not expected that some of the particles would be deflected at large angles or bounce back, as this implied that the positive charge in an atom was not uniformly distributed.

Conclusion:

In conclusion, the very small deflection of the beam was expected in the Geiger-Marsden experiment due to the distribution of charge in an atom and the reduction of electric field inside the atom. However, the unexpected results of the experiment led to the discovery of the nucleus and the development of the modern atomic model.

Answer is D

A/C to Bohr model ... mvr=nh/2π ... n=1,2,3...

The kinetic energy is zero and the electrical potential equals the initial kinetic energy supplied

If that is so grant us some suggestion! Or Balmer sequence (2nd sequence from electrons laying off to n = 2 from bigger than 2) longest wavelength [velocityconstant = frequency x wavelength] is smallest frequency [power = hconstant x frequency] is least enegy is from transition n = 3 to n = 2 or Google it 656.3 nm

Explanation:

The given question is related to the concept of atomic spectra. Atomic spectra is a characteristic property of every element which is used to identify the element. It is produced when an atom absorbs or emits energy as electromagnetic radiation.

The correct option is A, i.e., each element is associated with a characteristic spectrum of radiation. This means that every element emits or absorbs radiation of a unique wavelength that is specific to that particular element.

The characteristic spectrum of radiation is the set of wavelengths at which an element emits or absorbs radiation. There are three types of atomic spectra:

1. Continuous spectrum: A continuous spectrum is produced when a solid, liquid or dense gas is heated and the atoms in the material emit radiation at all wavelengths. This type of spectrum is not specific to any particular element.

2. Emission spectrum: An emission spectrum is produced when an element is heated or excited with energy, and the electrons in the atom jump to higher energy levels. When these electrons fall back to their original energy levels, they emit energy as radiation. The wavelengths of this radiation are specific to that particular element.

3. Absorption spectrum: An absorption spectrum is produced when an element absorbs certain wavelengths of radiation. When white light is passed through a sample of a specific element, certain wavelengths of light are absorbed by the atoms in the material, leaving dark lines in the spectrum. These dark lines are specific to that particular element.

In summary, the correct option is A because every element is associated with a characteristic spectrum of radiation, which is used to identify the element.

Bohr Model Hypothesis and Stable Electron Orbit

Bohr model hypothesis is a model of the atom proposed by Niels Bohr in 1913. It was one of the earliest attempts to explain the structure of atoms and their behavior. The model was based on the assumption that electrons orbit the nucleus in circular paths.

The correct statement about Bohr model hypothesis is:

- Electron in a stable orbit does not radiate electromagnetic waves.

Explanation:

- Electrons in atoms can exist only in certain discrete energy levels. According to Bohr's model, electrons in atoms move around the nucleus in stable orbits, each with a specific energy level.
- Electrons in stable orbits do not emit electromagnetic waves because they are in a stable state and have a fixed amount of energy.
- However, when an electron transitions from a higher energy level to a lower energy level, it emits a photon of light.
- This is because the energy lost by the electron is emitted as a photon of light. The energy of the photon is equal to the difference in energy between the two energy levels.
- Therefore, the Bohr model hypothesis proposed that the electron does not continuously lose energy as it moves in a circular orbit around the nucleus, but instead only loses energy when it transitions between energy levels.

Conclusion:

Bohr model hypothesis is an important model that helps explain the behavior of atoms. The model is based on the assumption that electrons move around the nucleus in stable orbits and only emit electromagnetic waves when they transition between energy levels. The correct statement about the model is that electrons in a stable orbit do not radiate electromagnetic waves.

The correct answer is option 'C' - heat flux.

Heat transfer is the process by which thermal energy is exchanged between objects or systems due to a temperature difference. The rate at which heat is transferred per unit area is known as the heat flux.

Heat flux is a measure of how much heat is transferred through a given area in a given amount of time. It is expressed in units of watts per square meter (W/m²) or calories per square centimeter per second (cal/cm²/s).

Now let's break down the options and understand why heat flux is the correct answer:

a) Temperature gradient: The temperature gradient refers to the change in temperature per unit length or distance. It represents how temperature changes with respect to position. While temperature gradient is related to heat transfer, it does not directly measure the rate of heat transfer per unit area.

b) Thermal conductivity: Thermal conductivity is a property of a material that describes how well it conducts heat. It is the measure of the ability of a material to conduct heat through it. While thermal conductivity is important in determining the rate of heat transfer, it is not the rate of heat transfer per unit area itself.

c) Heat flux: Heat flux is the rate of heat transfer per unit area. It quantifies the amount of heat energy transferred across a given surface area in a given time. It represents the flow of heat through a surface and is directly related to the temperature difference across the surface and the thermal conductivity of the material.

d) Specific heat: Specific heat is the amount of heat energy required to raise the temperature of a unit mass of a substance by a certain amount. It is an intrinsic property of a substance and is not directly related to the rate of heat transfer per unit area.

In summary, the rate of heat transfer per unit area is called heat flux. It represents the flow of heat through a surface and is determined by the temperature difference and thermal conductivity.

In Thomson's model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged “plums” surrounded by positively charged “pudding”. The 1904 Thomson model was disproved by Hans Geiger's and Ernest Marsden's 1909 gold foil experiment.

Answer:



To produce an emission spectrum of hydrogen, the hydrogen gas needs to be in a glowing gaseous form. This is because the emission spectrum of an element is produced when the electrons in the atoms of that element are excited to higher energy levels and then fall back to lower energy levels, emitting photons of specific wavelengths in the process.



Glowing Gaseous Form

When hydrogen gas is in a glowing gaseous form, the atoms are excited by an external energy source such as an electric discharge or a flame. This excitation causes the electrons in the hydrogen atoms to move to higher energy levels. As the excited electrons return to their original energy levels, they release energy in the form of photons. The photons emitted have specific wavelengths corresponding to the energy difference between the excited and ground states of the hydrogen atom.

Emission Spectrum

The emitted photons create a spectrum of discrete lines, known as an emission spectrum. These lines are unique to each element and can be used to identify the presence of that element. In the case of hydrogen, the emission spectrum consists of several series of lines, with each series corresponding to a different energy transition within the hydrogen atom.

Other Options

The other options mentioned in the question, such as cold and white light shining through, cool liquid form, and hot and white light shining through, are not suitable for producing an emission spectrum of hydrogen.

- Cold and white light shining through: White light is a combination of all visible wavelengths, and shining it through a cold hydrogen gas would not result in the emission of specific wavelengths characteristic of hydrogen.

- Cool liquid form: When hydrogen is in a cool liquid form, the atoms are not excited, and therefore, no emission spectrum is produced.

- Hot and white light shining through: Similar to the cold and white light scenario, shining white light through hot hydrogen gas would not produce specific wavelengths characteristic of hydrogen.

Conclusion

In conclusion, to produce an emission spectrum of hydrogen, the hydrogen gas must be in a glowing gaseous form. This allows for the excitation of the hydrogen atoms and the subsequent emission of photons with specific wavelengths, creating the characteristic emission spectrum of hydrogen.

Linear Dependence on Thickness t in Particle Scattering

Particle scattering refers to the process of a particle being deflected or redirected from its original trajectory after interacting with another particle or a field. In experiments involving particle scattering, the number of particles scattered at moderate angles is found to be proportional to the thickness t of the scattering material for small t values. This linear dependence on t provides a clue about the nature of the scattering process.

Predominance of Single Collision

The linear dependence of particle scattering on small thickness t suggests that the scattering is predominantly due to a single collision between the incident particle and the scattering material. This means that the incident particle interacts with only one scattering center or atom in the material and is deflected by a small angle. The probability of the incident particle interacting with multiple scattering centers and undergoing multiple collisions is low and does not significantly contribute to the overall scattering.

Explanation of Option A

Option A states that scattering is predominantly due to a single collision. This is consistent with the linear dependence of scattering on small thickness t, as explained above. Therefore, option A is the correct answer.

Conclusion

The linear dependence of particle scattering on small thickness t provides a clue about the nature of the scattering process. In particular, it suggests that scattering is predominantly due to a single collision between the incident particle and the scattering material. This information can be useful in designing experiments and understanding the behavior of particles in various materials.