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SMC|Academic Programs|Physical Sciences|Currents, wires and bulbs

Currents, wires and bulbs

1. Make a two battery circuit with one round bulb. Place a compass on the table, then lower a straight, tightly stretched part of a clip lead down onto the compass. Measure the deflection when the wire is lowered parallel to the compass needle and when the wire is lowered perpendicular to the compass needle.
  Deflection
wire parallel to compass needle  
wire perpendicular to compass needle  

2. Once you've found the orientation for the largest deflection, reverse the batteries.

Q: What happens to the compass deflection angle?

 

3. You are to measure the deflection for the circuit first with a round bulb in the circuit, then a long bulb.

  Deflection
round bulb  
long bulb  

 

Q: Which bulb has a greater deflection?

Q: Which bulb is brighter?

Q: Which bulb has more electrons flowing through it every second?

Are your answers above consistent with each other? Explain.

 

4. Add in two extra lengths of clip leads (making the circuit longer).

Q: How does the compass deflection change?

Q: How does the bulb brightness change?

5. Remove the bulb from the circuit so that two wires connect a single battery in a complete circuit (a "short circuit"). DON'T USE BOTH BATTERIES IN THE SHORT CIRCUIT.

Q: What is the compass deflection for the short circuit?

 

Now connect as many clip leads as possible into the short circuit (to make it as long as possible.

Q: What is the compass deflection for the longer short circuit?

 

6. Connect the thin nichrome wire to the two batteries using the clip leads. (Just place it in the circuit where the bulb would normally be.) Carefully feel how the temperature of the nichrome wire changes when the length of nichrome between the leads is shortened and lengthened.

Q: Which length of nichrome gets hotter - short or long?

 

Measure the deflections of the compass for  lengths of the thin nichrome wire. DON'T PLACE THE COMPASS UNDER THE NICHROME. PLACE IT UNDER THE CLIP LEADS LEADING TO THE NICHROME.

  Deflection
short length of thin nichrome (4 cm)  
long length of thin nichrome (8 cm)  

7. Measure the deflections of the compass for  lengths of the  thick nichrome wire.

  Deflection
short length of thick nichrome (4 cm)  
long length of thick nichrome (8 cm)  

Enter all your data into the following table:

round bulb deflection:

long bulb deflection:

short thin nichrome deflection:

long thin nichrome deflection:

short thick nichrome deflection:

long thick nichrome deflection:

short-circuit (two wires):

short-circuit (lots of wires):

8. Predict magnitudes of  the compass deflections at three different places in a two battery series circuit that has one round bulb in it. The places to predict are: A (the lead between the two batteries), B (between the negative terminal of one of the batteries and the bulb) and C (between the bulb and the positive terminal of the other battery). Draw the circuit below and write your prediction (Eg. A > B > C)

 

 

 

 

 

 

Prediction: 

Now measure the deflections

  Deflection
A  
B  
C