Electrical Charges and Attraction

[csfyp.mail]

Hi, Pls I'd like to find out if 2 electrical charges (same charge but different voltages) would attract or repel. For example -600VDC and -100VDC.

I've always thought like charges repel and unlike charges attract. But I'm reading up on something that says the above would attract and become -600VDC.

Pls can someone explain why this is the case. Thanks

 

[berkeman]

Hi, Pls I'd like to find out if 2 electrical charges (same charge but different voltages) would attract or repel. For example -600VDC and -100VDC.

I've always thought like charges repel and unlike charges attract. But I'm reading up on something that says the above would attract and become -600VDC.

Pls can someone explain why this is the case. Thanks

Welcome to the PF.

Charges do not have "voltage" as you have written. Charges are measured in units of Coulombs, and the electric fields that they cause will be the origin in changes in voltage (electrical potential).

Can you please copy the exact wording and figure from your textbook that have you confused?

 

[csfyp.mail]

Welcome to the PF.

Charges do not have "voltage" as you have written. Charges are measured in units of Coulombs, and the electric fields that they cause will be the origin in changes in voltage (electrical potential).

Can you please copy the exact wording and figure from your textbook that have you confused?

This is it...

"A metallic roller called the developing roller inside an EP cartridge acquires a – 600VDC charge (called a bias voltage) from the HVPS. The toner sticks to this roller because there is a magnet located inside the roller and because of the electrostatic charges between the toner and the developing roller. While the developing roller rotates toward the photo-sensitive drum, the toner acquires the charge of the roller (–600VDC). When the toner comes between the developing roller and the photosensitive drum, the toner is attracted to the areas that have been exposed by the laser (because these areas have a lesser charge, –100VDC). The toner also is repelled from the unexposed areas (because they are at the same –600VDC charge, and like charges repel)."


EP - Electrophotographic
HVPS - High Voltage Power Supply

Thanks

 

[berkeman]

This is it...

"A metallic roller called the developing roller inside an EP cartridge acquires a – 600VDC charge (called a bias voltage) from the HVPS. The toner sticks to this roller because there is a magnet located inside the roller and because of the electrostatic charges between the toner and the developing roller. While the developing roller rotates toward the photo-sensitive drum, the toner acquires the charge of the roller (–600VDC). When the toner comes between the developing roller and the photosensitive drum, the toner is attracted to the areas that have been exposed by the laser (because these areas have a lesser charge, –100VDC). The toner also is repelled from the unexposed areas (because they are at the same –600VDC charge, and like charges repel)."


EP - Electrophotographic
HVPS - High Voltage Power Supply

Thanks

Ah, that makes more sense. They are using the word "charged" in the context of charging up the capacitances of the roller and drum. The charge on a capacitor is Q = C*V, where C is the capacitance, and V is the voltage.

The explanation is not very precisely worded, unfortunately. The explanation at wikipedia.org is better:

http://en.wikipedia.org/wiki/Photocopier

.

 

[csfyp.mail]

Alright, Thanks.