# Current, voltage : brightness of bulb in parallel or series

• Barclay
In summary, the conversation discusses the differences between series and parallel circuits and how they affect the brightness of light bulbs. In a parallel circuit, the bulb with the lower resistance will be brighter because it allows more current to pass through. In a series circuit, the bulb with the higher resistance will be brighter because it requires a higher voltage to allow the same amount of current to pass through. The relevant equations are P=IV, P=V^2/R, and R=V^2/P.
Barclay
Member advised to use the homework template for posts in the homework sections of PF.
Hello I'm working through a book (with answers) but am struggling with voltage, current, resistance and circuits. Please check my understanding below and let me know if I've finally understood. Thank you.
In particular I'm confused in Q2

Q1.
A student connects light bulbs, A and B, and parallel across a battery. Bulb A is brighter than bulb B. Which bulb has the higher resistance? Explain.
ANSWER IN BOOK IS BULB B

Because it is a parallel circuit the same voltage MUST pass across each bulb i.e. there is a equal PUSH of current through each bulb. [I've learned to think of voltage as a PUSH]

Bulb B is dimmer because it has a higher resistance. For the same voltage (PUSH) it resists the passage of current (electrons) so remains dim.

Bulb A is brighter because it has a lower resistance. For the same voltage (PUSH) it does not resist the passage of current (because it has low resistance) so becomes bright.

The relevant equation is P =IV

Say for Bulb A the current passing through is 6 A with a voltage (PUSH) of 10 V so the power the bulb receives to light the bulb is P=IV P = 6 x 10 P = 60 watts [THAT'S A BRIGHT BULB]

Say for Bulb B the current passing through is only 1 A (because of its higher resistance) with a voltage (PUSH) of 10 V so the power the bulb receives to light the bulb is P=IV P = 1 x 10 P = 10 watts [THAT'S A DIM BULB]Q2. If the student connects the same bulbs in series with the same battery, which bulb will be brighter? Explain.
ANSWER IN BOOK IS BULB B will be brighter.

Because it is a series circuit the same current MUST pass through each bulb. The voltage across the components is shared in the ratio of the resistance of the components. The component with the higher resistance must have more voltage (PUSH) passing across it to deliver the same current.

Bulb B has the higher resistance so requires a high voltage across it (giving a big PUSH to the electrons) to allow current (electrons) to pass through it.

Bulb A has the low resistance so requires a low voltage across it to allow the same current (electrons) to pass through it.

In Bulb B with large voltage and the same current there will be large energy so the bulb will be brighter.

The relevant equation is P =IV

Say for Bulb B the current passing through is 10 A with a voltage (PUSH) of 100 V so the power the bulb receives to light the bulb is P=IV P = 10 x 100 P = 1000 watts [THAT'S A BRIGHT BULB]

For Bulb A the current passing through is also 10 A (because it is a series circuit) but a voltage (PUSH) of only 10 V is required (because it is a bulb of low resistance) so the power the bulb receives to light the bulb is P=IV P = 10 x 10 P = 100 watts [THAT'S A DIM BULB]

Yep

Barclay said:
The relevant equation is P =IV

That and Ohms law gets you to...

P = V2/R
or
R = V2/P

The brighter the bulb the more power it uses and the smaller is R.

## 1. What is the difference between current and voltage?

Current and voltage are both important electrical properties, but they have different meanings. Current refers to the flow of electric charge, while voltage refers to the potential difference between two points in an electrical circuit. In simpler terms, current is the movement of electrons, while voltage is the force that drives those electrons.

## 2. How is the brightness of a bulb affected in a parallel circuit?

In a parallel circuit, the brightness of a bulb is not affected by other bulbs connected in the same circuit. This is because each bulb has its own separate path to the power source, allowing it to receive the same amount of voltage and produce the same level of brightness as if it were the only bulb in the circuit.

## 3. Does adding more bulbs in series increase the overall brightness?

In a series circuit, the more bulbs you add, the dimmer the bulbs will become. This is because the voltage is shared between all the bulbs in the circuit, resulting in a lower voltage for each bulb. As a result, the overall brightness decreases.

## 4. How does the current change in a parallel circuit?

In a parallel circuit, the current is divided among the branches of the circuit. This means that the total current flowing into the circuit is equal to the sum of the currents flowing through each individual branch. So, if you add more bulbs in parallel, the total current in the circuit will increase.

## 5. Why is a parallel circuit preferred over a series circuit for household wiring?

A parallel circuit is preferred for household wiring because it allows for multiple devices to be connected to the same power source without affecting each other's operation. In a series circuit, if one device fails, the entire circuit is broken and all devices will stop working. In a parallel circuit, if one device fails, the other devices will still function normally.

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