Question

What will happen if you interchange the position of the galvanometer and the battery??

Answer 1

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ᴛʜᴇʀᴇ ᴡɪʟʟ ʙᴇ ɴᴏ ᴄʜᴀɴɢᴇ ɪɴ ᴛʜᴇ ᴘᴏꜱɪᴛɪᴏɴ ᴏꜰ ɴᴜʟʟ ᴘᴏɪɴᴛ, ꜰᴏʀ ᴀ ᴄᴇʀᴛᴀɪɴ ᴘᴏɪɴᴛ, ᴛʜᴇ ᴄᴜʀʀᴇɴᴛ ᴛʜʀᴏᴜɢʜ ᴛʜᴇ ʙᴀᴛᴛᴇʀʏ ᴡɪʟʟ ʙᴇ 0/ɴᴏ ᴄᴜʀʀᴇɴᴛ ᴡɪʟʟ ʙᴇ ᴅʀᴀᴡɴ ꜰʀᴏᴍ ᴛʜᴇ ʙᴀᴛᴛᴇʀʏ.

Answer 2

ᴛʜᴇʀᴇ ᴡɪʟʟ ʙᴇ ɴᴏ ᴄʜᴀɴɢᴇ ɪɴ ᴛʜᴇ ᴘᴏꜱɪᴛɪᴏɴ ᴏꜰ ɴᴜʟʟ ᴘᴏɪɴᴛ, ꜰᴏʀ ᴀ ᴄᴇʀᴛᴀɪɴ ᴘᴏɪɴᴛ, ᴛʜᴇ ᴄᴜʀʀᴇɴᴛ ᴛʜʀᴏᴜɢʜ ᴛʜᴇ ʙᴀᴛᴛᴇʀʏ ᴡɪʟʟ ʙᴇ 0/ɴᴏ ᴄᴜʀʀᴇɴᴛ ᴡɪʟʟ ʙᴇ ᴅʀᴀᴡɴ ꜰʀᴏᴍ ᴛʜᴇ ʙᴀᴛᴛᴇʀʏ.

For maximum sensitivity, the galvanometer should be connected across the ratio arms and the battery across the other two junctions of the bridge. As in this diagram from Wikipedia. Battery to points A & C. Galvo to points D & B. You could interchange battery and galvo but this means a lower galvo deflection for a given amount of imbalance. There is also more of a risk of overheating the ratio arms.

Battery polarity does not matter as no current flows through the galvanometer when the bridge is balanced, but you may want to experiment and have it connected so that the galvo deflects to the right when the ‘known’ arm is increased. i.e. dials turned to the right if using a resistance substitution box, or a purpose built bridge. I found this makes balancing more intuitive.