 # Ohm’s law – problems and solutions

Ohm’s law – problems and solutions

1.

Based on the table below, the relation between voltage (V), electric current (I) and resistance (R) is….. Solution :

Ohm’s law :

V = I R or R = V / I

R1 = V / I = 1.50 / 0.08 = 18.75 Ohm

R2 = V / I = 2.80 / 1.50 = 2.87 Ohm

R3 = V / I = 3.99 / 2.10 = 1.9 Ohm

Based on the table, the relationship between V, I and R is the value of R inversely proportional to V and I. That means the larger the V and I, the smaller R.

The value of V / I is not constant so it does not illustrate Ohm’s law. According to Ohm’s law, the value of V / I must be constant.

2. Which graph indicates the relationship between the potential difference with the electric current? Solution :

A

3. Based on the data in the following table of the experiment result, it can be concluded that the electric current … Solution :

Based on the data in the table, the greater the electrical voltage, the greater the electric current. Therefore it is concluded that the electric current is proportional to the voltage.

4. A device has a 150 Ohm resistance and a 2A electric current passes. The potential difference is…

Known :

Resistance (R) = 150 Ohm

The electric current (I) = 2 Ampere

Wanted: Voltage (V)

Solution :

V = I R

V = electric voltage, I = electric current, R = electric resistance

Voltage :

V = I R = (2 Ampere)(150 Ohm) = 300 Volt

5. The electric current in a resistor wire is 4 A. When both ends are given a potential of 12 Volts. What is the electrical resistance?

Known :

Electric current (I) = 4 Ampere

Voltage (V) = 12 Volt

Wanted : Electric resistance (R)

Solution :

Resistance :

R = V / I = 12 Volt / 4 Ampere = 3 Ohm

1. What is Ohm’s Law?
• Answer: 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 () of the conductor. Mathematically, it’s represented as .
2. If a resistor follows Ohm’s Law, what kind of relationship should we observe between voltage and current?
• Answer: We should observe a linear relationship. If you graph voltage against current, the slope of the line would represent the resistance, and the line would pass through the origin.
3. How does increasing the resistance in a circuit affect the current, assuming voltage remains constant?
• Answer: If the resistance increases while voltage remains constant, the current in the circuit will decrease, as per Ohm’s Law.
4. Why might Ohm’s Law not apply under certain conditions or for certain materials?
• Answer: Ohm’s Law applies to “ohmic” materials where resistance remains constant with changing voltage. However, for some materials and devices (like diodes, or at very high frequencies or temperatures), resistance may change with voltage or current, making the relationship non-linear.
5. What is the unit of resistance, and how is it defined in terms of Ohm’s Law?
• Answer: The unit of resistance is the ohm (Ω). One ohm is defined as the resistance that will allow one ampere of current to flow when one volt is applied across it.
6. If two resistors in series both strictly obey Ohm’s Law, will the combination also obey Ohm’s Law?
• Answer: Yes, the combination will also obey Ohm’s Law. The total resistance in series is the sum of the individual resistances, and the current through both will be the same. The voltage across the combination will be the sum of the voltages across each resistor.
7. How does the resistance of a wire depend on its length and cross-sectional area?
• Answer: The resistance of a wire is directly proportional to its length and inversely proportional to its cross-sectional area. Thus, a longer wire will have greater resistance, and a thicker wire will have less resistance.
8. If the voltage across a resistor is doubled, how does the current change, assuming the resistor remains ohmic?
• Answer: If the resistor remains ohmic (and thus follows Ohm’s Law), doubling the voltage will also double the current.
9. Can a component with zero resistance be realized in practice?
• Answer: In practical everyday scenarios, a component with zero resistance, or a “superconductor”, cannot be easily realized. However, certain materials at extremely low temperatures can become superconductors and offer zero resistance to current flow.
10. What is the power dissipation of a resistor in terms of Ohm’s Law?
• Answer: The power () dissipated by a resistor is given by or , derived from the combination of Ohm’s Law and the power formula .