Science: Ohm's Law and Electric Circuits
Using voltage, current, and resistance in simple circuits
Science: Ohm's Law and Electric Circuits
Using voltage, current, and resistance in simple circuits
Science - Grade 9-12
- 1
A resistor has a resistance of 6 ohms and a current of 2 amperes flows through it. Find the voltage across the resistor.
Use Ohm's law: V = IR.
The voltage is 12 volts because V = IR = 2 A x 6 ohms = 12 V. - 2
A 24 volt battery is connected to a resistor. The current in the circuit is 3 amperes. Find the resistance.
The resistance is 8 ohms because R = V / I = 24 V / 3 A = 8 ohms. - 3
A circuit has a resistance of 15 ohms and a voltage of 45 volts. Find the current.
Rearrange Ohm's law to solve for current.
The current is 3 amperes because I = V / R = 45 V / 15 ohms = 3 A. - 4
A lamp draws 0.5 amperes from a 120 volt source. What is the lamp's resistance?
The lamp's resistance is 240 ohms because R = V / I = 120 V / 0.5 A = 240 ohms. - 5
A device has a resistance of 10 ohms and is connected to a 9 volt battery. Find the current in the device.
Current equals voltage divided by resistance.
The current is 0.9 amperes because I = V / R = 9 V / 10 ohms = 0.9 A. - 6
Two resistors of 4 ohms and 6 ohms are connected in series. Find the total resistance.
The total resistance is 10 ohms because resistances in series add directly: 4 ohms + 6 ohms = 10 ohms. - 7
Two resistors of 12 ohms and 18 ohms are connected in parallel. Find the equivalent resistance.
For parallel resistors, add the reciprocals first.
The equivalent resistance is 7.2 ohms because 1 / Req = 1 / 12 + 1 / 18 = 5 / 36, so Req = 36 / 5 = 7.2 ohms. - 8
A 20 volt source is connected to a series circuit containing a 3 ohm resistor and a 7 ohm resistor. Find the total current in the circuit.
The total current is 2 amperes because the total resistance is 3 ohms + 7 ohms = 10 ohms, and I = V / R = 20 V / 10 ohms = 2 A. - 9
A 12 volt battery is connected to two parallel resistors of 6 ohms and 3 ohms. Find the equivalent resistance of the circuit.
The equivalent resistance of parallel branches is less than the smallest branch resistance.
The equivalent resistance is 2 ohms because 1 / Req = 1 / 6 + 1 / 3 = 1 / 6 + 2 / 6 = 3 / 6 = 1 / 2, so Req = 2 ohms. - 10
A resistor has 18 volts across it and carries 3 amperes of current. How much power does it use?
The power is 54 watts because P = VI = 18 V x 3 A = 54 W. - 11
An electric heater uses 1200 watts when connected to a 120 volt outlet. Find the current drawn by the heater.
Use the power formula P = VI.
The current is 10 amperes because I = P / V = 1200 W / 120 V = 10 A. - 12
A phone charger delivers 5 volts and 2 amperes. Find its power output.
The power output is 10 watts because P = VI = 5 V x 2 A = 10 W. - 13
A student says that increasing resistance in a circuit with the same voltage will increase the current. Explain whether this statement is correct.
Look at the relationship between current and resistance in Ohm's law.
The statement is incorrect. If the voltage stays the same, increasing resistance decreases current because I = V / R. - 14
Describe the difference between a series circuit and a parallel circuit in terms of current and voltage.
In a series circuit, the same current flows through each component and the voltage is shared among the components. In a parallel circuit, each branch has the same voltage and the current splits among the branches. - 15
A 9 volt battery is connected to a resistor and the current is measured as 0.3 amperes. If the battery voltage stays the same and the resistance is doubled, what will the new current be?
Start by finding the original resistance or reason from the inverse relationship.
The new current will be 0.15 amperes. Doubling the resistance cuts the current in half when the voltage stays constant, according to I = V / R.