What value of a series resistor is required to limit the current through an LED to 20 mA with a forward voltage drop of 2.0 V, when connected to a 10-V supply?a)600 b)200 c)800 d)400 Correct answer is option 'D'. Can you explain this answer?

Question

Answer

Concept:

When LED conducts, it is replaced by its cut-in voltage with a limiting resistor connected in series with it.

where, V_S = Source voltage
V_γ = Cut-in voltage
R = Limiting resistor
I = Current

Calculation:
Given, V_S = 10V
Vγ = 2V
I = 20mA

Answer

Concept:

When LED conducts, it is replaced by its cut-in voltage with a limiting resistor connected in series with it.

where, V_S = Source voltage
V_γ = Cut-in voltage
R = Limiting resistor
I = Current

Calculation:
Given, V_S = 10V
Vγ = 2V
I = 20mA

Answer

To calculate the value of the series resistor required to limit the current through an LED to 20 mA, we can use Ohm's Law. Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.

Given:
Forward voltage drop of the LED (Vf) = 2.0 V
Desired current through the LED (If) = 20 mA = 0.02 A
Supply voltage (Vs) = 10 V

We can calculate the value of the series resistor (Rs) using the formula:

Rs = (Vs - Vf) / If

Substituting the given values:

Rs = (10 V - 2.0 V) / 0.02 A
Rs = 8.0 V / 0.02 A
Rs = 400 Ω

Therefore, the value of the series resistor required to limit the current through the LED to 20 mA with a forward voltage drop of 2.0 V, when connected to a 10-V supply, is 400 Ω.

Explanation:
- Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage across the two points and inversely proportional to the resistance.
- In this case, we are given the forward voltage drop of the LED (Vf), the desired current through the LED (If), and the supply voltage (Vs).
- To calculate the value of the series resistor (Rs), we use the formula Rs = (Vs - Vf) / If.
- By substituting the given values into the formula, we can calculate the value of Rs as 400 Ω.
- The series resistor is used to limit the current flowing through the LED and prevent it from exceeding the desired value.
- In this case, the value of Rs is chosen to ensure that the current through the LED is 20 mA when connected to a 10-V supply.

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