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Define the distance of closest approach.
The distance of closest approach is the minimum distance between the nucleus and an incoming particle, such as an alpha particle, during a collision. At this point, the particle's kinetic energy is completely converted into electrostatic potential energy due to the nucleus's repulsion. For more visiRead more
The distance of closest approach is the minimum distance between the nucleus and an incoming particle, such as an alpha particle, during a collision. At this point, the particle’s kinetic energy is completely converted into electrostatic potential energy due to the nucleus’s repulsion.
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What is the minimum distance, in terms of focal length of lens, between an object and its real image formed by a convex lens?
The minimum distance between an object and its real image formed by a convex lens is twice the focal length. This occurs when the object is placed at twice the focal length from the lens. For more visit here: https://www.tiwariacademy.com/ncert-solutions/class-12/physics/chapter-9/
The minimum distance between an object and its real image formed by a convex lens is twice the focal length. This occurs when the object is placed at twice the focal length from the lens.
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When an electron falls from a higher energy to a lower energy level, the difference in the energies appears in the form of electromagnetic radiation. Why cannot it be emitted as other forms of energy?
The energy difference during an electron's transition is emitted as electromagnetic radiation because it arises from changes in the electron's energy levels, governed by quantum mechanics. Other forms of energy, like kinetic or thermal energy, do not align with the quantized nature of electronic traRead more
The energy difference during an electron’s transition is emitted as electromagnetic radiation because it arises from changes in the electron’s energy levels, governed by quantum mechanics. Other forms of energy, like kinetic or thermal energy, do not align with the quantized nature of electronic transitions.
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Define heat current and thermal resistance. Write mathematical expressions for them in terms of thermal conductivity K.
Heat Current (Q): Heat current refers to the rate at which heat energy flows through a material. It depends on the temperature difference across the material, its area, the length of the material, and its thermal conductivity. Mathematical Expression for Heat Current: The heat current Q is given byRead more
Heat Current (Q):
Heat current refers to the rate at which heat energy flows through a material. It depends on the temperature difference across the material, its area, the length of the material, and its thermal conductivity.
Mathematical Expression for Heat Current:
The heat current Q is given by Fourier’s Law of Heat Conduction:
Q = (K A (T1 – T2)) / L
Where:
– Q = Heat current (rate of heat flow) in watts (W)
– K = Thermal conductivity of the material (W/m·K)
– A = Cross-sectional area through which heat flows (m²)
– T1 – T2 = Temperature difference between the two ends of the material (K or °C)
– L = Length of the material through which heat flows (m)
Thermal Resistance (R):
Thermal resistance is a measure of a material’s resistance to the flow of heat. It depends on the material’s thermal conductivity, length, and area.
Mathematical Expression for Thermal Resistance:
The thermal resistance R is given by:
R = L / (K A)
Where:
– R = Thermal resistance (K·m²/W)
– L = Length of the material (m)
– K = Thermal conductivity of the material (W/m·K)
– A = Cross-sectional area (m²)
Relationship Between Heat Current and Thermal Resistance:
Using the expression for thermal resistance, the heat current can also be written as:
Q = (T1 – T2) / R
Where R is the thermal resistance of the material. This shows that heat current is directly proportional to the temperature difference and inversely proportional to the thermal resistance.
Summary:
– Heat current is the rate of heat transfer through a material, given by Q = (K A (T1 – T2)) / L.
– Thermal resistance is the resistance to heat flow, given by R = L / (K A).
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What do you mean by variable state and steady state in thermal conduction? Define temperature gradient.
Variable State in Thermal Conduction In thermal conduction, a variable state refers to a situation where the temperature distribution within the material is changing with time. In this state, the temperature at any point in the material is not constant, and the heat flow is not steady. This usuallyRead more
Variable State in Thermal Conduction
In thermal conduction, a variable state refers to a situation where the temperature distribution within the material is changing with time. In this state, the temperature at any point in the material is not constant, and the heat flow is not steady. This usually occurs when the material is initially heated or cooled, and the temperature difference between different parts of the material is evolving over time until it reaches equilibrium.
– For instance, suppose a metal rod is heated on one end; the temperature changes at different points along the rod with time since heat is being transferred from the hot end to the cooler end. The gradient will be high in the beginning, and with the passage of time, the gradient will decrease to the point when the system achieves equilibrium.
Steady State in Thermal Conduction:
In thermal conduction, a steady state is when the temperature distribution in the material becomes constant over time. The temperature at any point in the material no longer changes, which means there is no further change in temperature with respect to time. The heat flow becomes constant, and the system has reached thermal equilibrium.
Example: For instance, if the temperature has stabilized such that no temperature variation is noticed in the rod as described earlier, then the system is in a steady state. The amount of heat going into one end is the same as the amount of heat going out the other end.
Temperature Gradient:
Temperature gradient is the measure of how temperature changes over a given distance in a material. It is defined as the rate of change of temperature with respect to distance. It is often measured in units of °C/m or K/m.
– Mathematical Expression: The temperature gradient ∇T can be mathematically expressed as:
∇T = ΔT / Δx
Where:
– ∇T = Temperature gradient (°C/m or K/m)
– ΔT = Temperature difference between two points in the material (°C or K)
– Δx = Distance between the two points (m)
In a steady-state conduction, the temperature gradient is constant and linear, so that the rate of temperature change is uniform throughout the material. In a variable state, the temperature gradient changes with time as the material approaches a new thermal equilibrium.
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