How does brightness of light globes change when different switches are closed?

[TyErd]

Homework Statement

1. Describe and explain how the brightness of each globe will be affected if only Sa is switched on.
2. Describe and explain the effects of the light globes if only Sb is switched on.

Homework Equations

None

The Attempt at a Solution

No working out required I believe.

 

[rl.bhat]

If only Sa is closed, what happens to the total resistance of the circuit?
What is the current in each lamp?
If Sb is closed, What change in the resistance you observe in the circuit?

 

[TyErd]

for when Sa is closed,the total resistance doesn't change because their was current flowing through the globes but from a different path, current in each lamp would decrease because it is being split up now that there is an extra path?

 

[rl.bhat]

for when Sa is closed,the total resistance doesn't change because their was current flowing through the globes but from a different path, current in each lamp would decrease because it is being split up now that there is an extra path?

It is not correct. Since the total resistance remains the same, the current drawn from the cell is the same. In both the cases , it equally branches out in two parallel circuits. So in each the branch the current is I/2.

 

[TyErd]

Okay, i understand, now for when only Sb is closed,...im not really sure

 

[rl.bhat]

Okay, i understand, now for when only Sb is closed,...im not really sure

One bulb is short circuited. Leaving that bulb, calculated the total resistance and the current in each bulb.

 

[TyErd]

why is it short circuited?

 

[rl.bhat]

why is it short circuited?

All the current passes through the Sb. So the bulb will be off.

 

[TyErd]

does all current pass through Sb or does it divide into two paths?