Sislm818 發問於 科學及數學其他 - 科學 · 1 十年前

# F.2 IS - Electric current

1. Two bulbs are connected in series in the following diagram

If a thick copper wire is connected across A

a.What will happen to bulb B?

b.What will happen to bulb A?

c.What will happen to the reading of the ammeter?

2.Ben has connected the circult as shown in the following diagram

a.i.What happens when switch S is closed?

ii.What happens when switch S is opened?

b.i.Ben thinks that the circult is properly connected because the switch can be used to switch on or off the bulb.Do you agree?

### 3 個解答

• 天同
Lv 7
1 十年前
最愛解答

1.a.What will happen to bulb B?

Since the copper wire by-passed bulb A, leaving only bulb B in the circuit. Bulb B will glow brighter.

b.What will happen to bulb A?

Bulb A will not glow. Iy has been by-passed by the copper wire. There is no current flowing through bulb A.

c.What will happen to the reading of the ammeter?

The reading will increase showing an increase of current.

2. (a)(i) What happens when switch S is closed?

The bulb will not glow, and the battery gets hot.

ii.What happens when switch S is opened?

The bulb glows.

Ben thinks that the circult is properly connected because the switch can be used to switch on or off the bulb.Do you agree?

No. Closing the switch causes a "short circuit". There is still current flowing through. Since the resistance of the circuit is low, the current flowing will be large, battery might be damaged.

• 1 十年前

(a)

Since The Bulb A Was Short-Circuit,So The Current Will Be Increase,SO The Bulb B Will More Brightless.

(b)

According To Ohms Law V=IR,Copper Wire Cause The Bulb A Short-Circuit,So the Bulb A Will Not Light Up(Very Very Little Amount To Bulb A)

(c)

Since The Copper Connect In Parallel,Than According To The Parallel-Resistance Law,1/R=1/R1+1/R2...+1/Rn,

So The Current Will Increase,When Combine With Bulb B In Series,

Since The Resistance Is Lower,So The Current Will Increase,Thus,The Ammeter Will Increase The Reading.

(2a.i.)

When The Switch Is Closed,Its Means The Two Poles Will Have Continuity To Let The Current Flows.So Therefore,After Closed The Switch,The Resistances Will Be Very Low,So That It Cause Short-Circuit.

(2a.ii.)

As The Photo,Switch Is Open,The Resistance Of The Switch Close To Infinity,So Therefore No Current Flow There,So The Bulb Will Light Up.

(2b.i.)

IT MUST WRONG.

Although The Switch Can Be Controlled The Bulb On And Off,But Will The Bulb Off,Its A Short-Circuit Actually,It Causes The Batteries Very Hot,Even Explode,The Wire Will Get Very Hot As Well.

The Switch Can Control The Bulb On And Off,But This Way Is UNSAFE.

• 1 十年前

1a.bulb b will increase brightness

1b.bulb a will be dimmed or extinguished