Question

Investigation B, The Braun Electroscope

       The Braun electroscope consists of a metal disc at the upper end of a metal rod insulated from the case of the instrument. The rod supports a light metal vane free to rotate about a horizontal axis. When the electroscope is charged the vane swings from its normal vertical position to a near equilibrium position. The angle it makes with the vertical is proportional to the charge of the electroscope.

1            A. Ground the electroscope by touching the disc.

B. Bring a negatively charged rod near the disc of the electroscope.

C. Remove the rod.

2            A. Ground the electroscope.

B. Bring a negatively charged rod near the disc of the electroscope.

C. Touch the rod to the disc. This is charging by contact.

D. Remove the rod.

3   A. Charge the electroscope as in 7, by contact.

B. Bring the negatively charged rod to within 5 cm. of the disc of the electroscope.

C. Bring the negatively charged rod as close to the disc as possible without a spark jumping from the rod to the disc.

D. Remove the rod.

4   A. Charge the electroscope as in 7, by contact.

B. Bring a positively charged rod to within about 5cm. of the disc of the electroscope.

C. Bring a positively charged rod as close to the disc of the electroscope as possible without a spark jumping from the rod

D. Remove the rod.

5     A. Ground the electroscope.

      B. Bring a negatively charged rod near the disc of the electroscope.

      C. keeping the rod near the disc, ground the telescope.

      D. Keeping the rod near the disc, removes the grounding connection.

      E. Remove the rod. The electroscope has been charged by induction.

6     A. Charge the electroscope by induction as 10 observing carefully the charging distance between rod and disc when the electroscope is grounded.

B. Bring a negatively charged rod near the disc. Draw diagrams for the following cases:

1) Rod beyond the charging distance.

2) Rod at charging distance.

3) Rod inside the charging distance.

C. Remove the rod.

7      A. Charge the electroscope by induction as in 10.

       B. Bring a positively charged rod near the electroscope.

       C. Remove the rod.

Note: the experiments above might be repeated, replacing a positive with a negative rod and a negative with a positive rod. In all cases the charge distribution would be opposite to that for the above experiments.

8. Charge the electroscope positively by induction. Record the electroscope positively by induction. Record the effect of bringing the hand near the knob of the electroscope.

Charge the electroscope negatively by induction. Record the effect of bringing the hand near the electroscope. Diagrams need not be drawn for this part.

I have no idea about this lab report!!~
The prof reuqire us to explain which situation !~~ Please help

Answer 1

3rd step

3   A. Charge the electroscope as in 7, by contact.

B. Bring the negatively charged rod to within 5 cm. of the disc of the electroscope.

C. Bring the negatively charged rod as close to the disc as possible without a spark jumping from the rod to the disc.

D. Remove the rod.

Explaination.

A. Disc is charged now

B. The +ve ions are attracted to the rod. Disc is still charged

C. The disc is still charged and no transfer of charge takes place as disc is not touched by rod.

D. Rod is removed and disc remains charged

4th step

4   A. Charge the electroscope as in 7, by contact.

B. Bring a positively charged rod to within about 5cm. of the disc of the electroscope.

C. Bring a positively charged rod as close to the disc of the electroscope as possible without a spark jumping from the rod

D. Remove the rod.

Explaination

A. Disc is charged.

B. The -ve ions are attracted to the rod. Disc is still charged

C. The disc is still charged and no transfer of charge takes place as disc is not touched by rod.

D. Rod is removed and disc remains charged

5th step

5     A. Ground the electroscope.

      B. Bring a negatively charged rod near the disc of the electroscope.

      C. keeping the rod near the disc, ground the telescope.

      D. Keeping the rod near the disc, removes the grounding connection.

      E. Remove the rod. The electroscope has been charged by induction.

Explaination.

A. Disc is made neutral

B. +ve ions in disc are attracted towards rod

C. When disc is grounded, the negative ions flow to the ground, creating an overall +ve charge on disc.

D. Disc is positively charged now

E. Thus disc can also be charged without physical contact of rod

6th step

6     A. Charge the electroscope by induction as 10 observing carefully the charging distance between rod and disc when the electroscope is grounded.

B. Bring a negatively charged rod near the disc. Draw diagrams for the following cases:

1) Rod beyond the charging distance.

2) Rod at charging distance.

3) Rod inside the charging distance.

C. Remove the rod.

Explaination

A. Disc is charged

B. +ve ions in disc are attracted towards rod

C. Rod is removed but disc remains neutral

7th step

7      A. Charge the electroscope by induction as in 10.

       B. Bring a positively charged rod near the electroscope.

       C. Remove the rod.

Explaination

A. Disc is charged by induction

B. -ve ions in disc are attracted towards rod

C. Disc remains charged.