Investigating flux density

Question 1

Describe the set up of the equipment?

Answer 1

• U magnet on zeroed top pan balance
• thick, current carrying copper wire place perpendicular to magnetic through the centre
• connected to variable resistor, and ammeter to measure current

Question 2

How is the current varied>

Answer 2

• variable resistor

Question 3

When is the balance zeroed?

Answer 3

• when thee is no current through the wire
• so that the mass reading is due to the electromagneti cforce only

Question 4

What is recorded? What is the independant and dependant variable?

Answer 4

• independant
  
  • current
• dependant
  
  • mass reading

Question 5

What is the procedure?

Answer 5

• balance zeroed then current switched on
• current and balance reading are recorded
• current increase
  
  • reading taken for at least six reading
  • repeats

Question 6

How is a uniform field created?>

Answer 6

• magnets have their poles on their faces and are fixed to a stell yoke, creating a magnetic field
• important to check the magnets attract to ensure a norht pole faces a south pole

Question 7

What must the structure of the wire be?

Answer 7

• thick and rigid
• supported horizontally

Question 8

How are the readings converted?>

Answer 8

• converted to force using F = mg

Question 9

How can magnetic flux density be worked out?

Answer 9

• graph of F against I
• because F = BIL, BI = gradient
• divide by lengtrh to get a vlue for B

Question 10

What is an alternative procedure for this experiment?

Answer 10

• vary length of wire perpendicular to the magnetic field by using different size hoops
  
  • adding additional yokes
• yoy could keep current and wire length the same and instread vary the magnetic field by changing the strength of magnets

Question 11

Why is a sensitive top pan balance useD?

Answer 11

• small forces
• sensitive to measure the force

Question 12

How does this relate to Newton’s third law?

Answer 12

• the magnetic force experienced by the wire will be equal in size, but in the opposite direction to the force on the permanant U-shaped magnetis

Question 13

What are the safety considerations?

Answer 13

• in order to produce measurable magnetic forces, relatively large currents have to be used
  
  • causes wire to heat up
  • so turns circuit off between readings
  • reduce degree of heating
• rheostat (electrical instrument used tocontrol current by varying resistance) needs to have a large power instrument to cope with the large current and heat produced