Resistance and Ohms law - Variation of Resistance with Temperature
1 Answer
Resistance is a fundamental property of an electrical component that measures its opposition to the flow of electric current. It's denoted by the symbol "R" and is measured in ohms (Ω). According to Ohm's Law, the relationship between voltage (V), current (I), and resistance (R) is given by the equation:
V = I * R
Where:
V is the voltage across the component,
I is the current flowing through the component,
R is the resistance of the component.
Ohm's Law implies that the resistance of a component remains constant as long as the temperature and other environmental conditions remain unchanged. However, in reality, the resistance of most materials changes with temperature due to the way the material's properties interact with the temperature.
The relationship between resistance and temperature can be understood using the following concepts:
Temperature Coefficient of Resistance (α):
Different materials exhibit different changes in resistance with temperature. The temperature coefficient of resistance (α) quantifies this change and is defined as the percentage change in resistance per degree Celsius change in temperature. It is usually expressed in units of 1/°C or %/°C.
The formula to calculate the resistance change due to temperature is:
ΔR = R₀ * α * ΔT
Where:
ΔR is the change in resistance,
R₀ is the initial resistance at a reference temperature (usually 20°C or 25°C),
α is the temperature coefficient of resistance,
ΔT is the change in temperature in degrees Celsius.
Positive and Negative Temperature Coefficients:
Materials can have positive or negative temperature coefficients of resistance. A positive coefficient means that the resistance increases with temperature, while a negative coefficient means that the resistance decreases with temperature.
Semiconductors and Thermistors:
In semiconductors, resistance is highly temperature-dependent. As the temperature increases, the number of charge carriers (electrons or holes) increases, leading to higher conductivity and lower resistance. Thermistors are a type of resistor with a particularly strong temperature-dependent resistance. They can be used as temperature sensors.
Metals and Alloys:
Most metals and alloys have a positive temperature coefficient of resistance. As temperature increases, the vibrations of atoms and ions increase, leading to greater scattering of charge carriers, and thus, higher resistance.
Superconductors:
Superconductors are materials that exhibit zero electrical resistance below a critical temperature. However, this is a special case and requires extremely low temperatures to achieve.
In summary, the resistance of most materials changes with temperature due to changes in the mobility of charge carriers, the arrangement of atoms, and other material-specific factors. The temperature coefficient of resistance helps quantify this change, and it's an important consideration in designing and using electronic components in various applications.
V = I * R
Where:
V is the voltage across the component,
I is the current flowing through the component,
R is the resistance of the component.
Ohm's Law implies that the resistance of a component remains constant as long as the temperature and other environmental conditions remain unchanged. However, in reality, the resistance of most materials changes with temperature due to the way the material's properties interact with the temperature.
The relationship between resistance and temperature can be understood using the following concepts:
Temperature Coefficient of Resistance (α):
Different materials exhibit different changes in resistance with temperature. The temperature coefficient of resistance (α) quantifies this change and is defined as the percentage change in resistance per degree Celsius change in temperature. It is usually expressed in units of 1/°C or %/°C.
The formula to calculate the resistance change due to temperature is:
ΔR = R₀ * α * ΔT
Where:
ΔR is the change in resistance,
R₀ is the initial resistance at a reference temperature (usually 20°C or 25°C),
α is the temperature coefficient of resistance,
ΔT is the change in temperature in degrees Celsius.
Positive and Negative Temperature Coefficients:
Materials can have positive or negative temperature coefficients of resistance. A positive coefficient means that the resistance increases with temperature, while a negative coefficient means that the resistance decreases with temperature.
Semiconductors and Thermistors:
In semiconductors, resistance is highly temperature-dependent. As the temperature increases, the number of charge carriers (electrons or holes) increases, leading to higher conductivity and lower resistance. Thermistors are a type of resistor with a particularly strong temperature-dependent resistance. They can be used as temperature sensors.
Metals and Alloys:
Most metals and alloys have a positive temperature coefficient of resistance. As temperature increases, the vibrations of atoms and ions increase, leading to greater scattering of charge carriers, and thus, higher resistance.
Superconductors:
Superconductors are materials that exhibit zero electrical resistance below a critical temperature. However, this is a special case and requires extremely low temperatures to achieve.
In summary, the resistance of most materials changes with temperature due to changes in the mobility of charge carriers, the arrangement of atoms, and other material-specific factors. The temperature coefficient of resistance helps quantify this change, and it's an important consideration in designing and using electronic components in various applications.