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Grain train
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THE LAST WORD Grain train I was weighing sugar into a plastic jug that had been recently washed and dried. There was too much sugar so I spooned some out with a teaspoon. The sugar sprayed off the spoon and coated the sides of the jug. Why?
n Drying the plastic jug by rubbing it with a tea towel has probably caused an exchange of charge between the towel and plastic, leaving the jug in an electrostatically charged state. Plastic is a good insulator, so it would take some time for this charge to leak to earth. A charged object creates an electric field around itself. The sugar grains start neutrally charged, containing a uniform mixture of positive and negative charges (see diagram, below). When the particles are placed near the charged walls of the jug, a) Particle in a neutral state
opposite charges are attracted to the side of the particle nearest to the charged object and like charges are repelled to the opposite side of the particle, creating an electric dipole. Because the opposite charges, which attract, are now closer together than the like charges, which repel, the attractive force is stronger. This means there is a net attractive force created between the particle and the wall. If the particle is small enough, this force can overcome its weight and make the sugar jump off the spoon and attach to the wall. A similar effect can be seen in the party trick of rubbing a balloon against your shirt until it becomes charged. Holding the charged balloon near someone’s hair should then cause their hair to lift from their head. This principle has many commercial applications, such as in the electrostatic precipitators used to remove fine particulates from flue gas at power stations. Simon Iveson Faculty of Engineering & Built Environment, The University of Newcastle, New South Wales, Australia
b) Particle near a charged state
Positive charge Negative charge
Jug wall
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
n This is due to electrostatic charge separation, causing the container and the small-grained insulating material within it to have opposite charges. A similar behaviour is seen when you draw a plastic comb through dry hair and it develops a charge that can attract charge-sensitive items, like flecks of paper.
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
Last_word_1040217
The exact mechanism is a source of some debate, with recent research suggesting that the electrons involved are moving to or from the water layer that is inevitably present on all materials exposed to ambient air. Either way, the net effect is that the fine powder is attracted to the oppositely charged container. Martin Falatic San Francisco, California, USA
Finally, the mention of St Elmo’s fire and the action of lightning rods is, I believe, not mainly connected to lightning strikes but to the prevention of such phenomena. In the physics lab, I used to demonstrate this using a Van de Graaff generator with a neon bulb attached to a nail, which was pointed at the charged sphere. In a darkened room, one can see both the ionisation glow from the tip of the nail (St Elmo’s fire) and the neon glow caused by the Bolted on flow of current. This partially Is the exact spot where a bolt of discharges the sphere and lightning will strike the earth pretty prevents spark discharges to much predetermined at the moment it a nearby earthed object, leaves a cloud? Or does it continuously demonstrating how a lightning change direction on the way down? conductor’s primary function (Continued) is to reduce the likelihood of strikes, as well as the usual n Earlier answers to the question explanation of reducing damage regarding the behaviour of if a strike occurs. lightning (21 January) raise Does anybody else have a number of issues. more information to answer First, one answer states that my questions? the base of a cloud is negatively Richard Horton charged and another that it is Whixley, North Yorkshire, UK positively charged: is only one of these correct or can it be either? Second, there is much mention This week’s question of negative flow, presumably of HAY FEVER FEVER electrons, in one direction and With the Australian spring comes positive flow (ions) in the seasonal allergic rhinitis, or hay opposite. But due to the huge fever. But why do humans have difference in mass between a physiological response to electrons and positive ions, pollen and dust? I can’t see any surely these two currents benefit to suffering from sore must take place over different eyes, a scratchy throat and nasal timescales and thus cause a congestion. So why does it occur? difference between cloud-toWendy Akers ground and ground-to-cloud Canberra, Australia “flashes”. Is this so?
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THE LAST WORD Grain train I was weighing sugar into a plastic jug that had been recently washed and dried. There was too much sugar so I spooned some out with a teaspoon. The sugar sprayed off the spoon and coated the sides of the jug. Why?
n Drying the plastic jug by rubbing it with a tea towel has probably caused an exchange of charge between the towel and plastic, leaving the jug in an electrostatically charged state. Plastic is a good insulator, so it would take some time for this charge to leak to earth. A charged object creates an electric field around itself. The sugar grains start neutrally charged, containing a uniform mixture of positive and negative charges (see diagram, below). When the particles are placed near the charged walls of the jug, a) Particle in a neutral state
opposite charges are attracted to the side of the particle nearest to the charged object and like charges are repelled to the opposite side of the particle, creating an electric dipole. Because the opposite charges, which attract, are now closer together than the like charges, which repel, the attractive force is stronger. This means there is a net attractive force created between the particle and the wall. If the particle is small enough, this force can overcome its weight and make the sugar jump off the spoon and attach to the wall. A similar effect can be seen in the party trick of rubbing a balloon against your shirt until it becomes charged. Holding the charged balloon near someone’s hair should then cause their hair to lift from their head. This principle has many commercial applications, such as in the electrostatic precipitators used to remove fine particulates from flue gas at power stations. Simon Iveson Faculty of Engineering & Built Environment, The University of Newcastle, New South Wales, Australia
b) Particle near a charged state
Positive charge Negative charge
Jug wall
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
n This is due to electrostatic charge separation, causing the container and the small-grained insulating material within it to have opposite charges. A similar behaviour is seen when you draw a plastic comb through dry hair and it develops a charge that can attract charge-sensitive items, like flecks of paper.
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
Last_word_1040217
The exact mechanism is a source of some debate, with recent research suggesting that the electrons involved are moving to or from the water layer that is inevitably present on all materials exposed to ambient air. Either way, the net effect is that the fine powder is attracted to the oppositely charged container. Martin Falatic San Francisco, California, USA
Finally, the mention of St Elmo’s fire and the action of lightning rods is, I believe, not mainly connected to lightning strikes but to the prevention of such phenomena. In the physics lab, I used to demonstrate this using a Van de Graaff generator with a neon bulb attached to a nail, which was pointed at the charged sphere. In a darkened room, one can see both the ionisation glow from the tip of the nail (St Elmo’s fire) and the neon glow caused by the Bolted on flow of current. This partially Is the exact spot where a bolt of discharges the sphere and lightning will strike the earth pretty prevents spark discharges to much predetermined at the moment it a nearby earthed object, leaves a cloud? Or does it continuously demonstrating how a lightning change direction on the way down? conductor’s primary function (Continued) is to reduce the likelihood of strikes, as well as the usual n Earlier answers to the question explanation of reducing damage regarding the behaviour of if a strike occurs. lightning (21 January) raise Does anybody else have a number of issues. more information to answer First, one answer states that my questions? the base of a cloud is negatively Richard Horton charged and another that it is Whixley, North Yorkshire, UK positively charged: is only one of these correct or can it be either? Second, there is much mention This week’s question of negative flow, presumably of HAY FEVER FEVER electrons, in one direction and With the Australian spring comes positive flow (ions) in the seasonal allergic rhinitis, or hay opposite. But due to the huge fever. But why do humans have difference in mass between a physiological response to electrons and positive ions, pollen and dust? I can’t see any surely these two currents benefit to suffering from sore must take place over different eyes, a scratchy throat and nasal timescales and thus cause a congestion. So why does it occur? difference between cloud-toWendy Akers ground and ground-to-cloud Canberra, Australia “flashes”. Is this so?
COPY SUB PAGE SUB OK for press