Step-up transformers are used for
- A.increasing electrical power
- B.decreasing electrical power
- C.decreasing voltage
- D.increasing voltage
Correct answer
Explanation
The correct answer is D, increasing voltage. A step-up transformer raises an alternating voltage, using more turns in its secondary coil than in its primary.
A transformer works on electromagnetic induction and only with alternating current. The ratio of voltages equals the ratio of turns: Vs/Vp = Ns/Np. In a step-up transformer Ns is greater than Np, so the output voltage rises while the current falls in the same proportion. At power stations, step-up transformers raise the voltage to hundreds of kilovolts so that a smaller current flows in the lines and less energy is lost as heat. Step-down transformers then lower it for homes.
A is wrong: a transformer cannot increase power; at best the output power equals the input power. B is wrong: an ideal transformer does not decrease power either; any loss is a small inefficiency, not its purpose. C is wrong: decreasing voltage is the job of a step-down transformer.
Exam tip: Step-up raises voltage and lowers current; power stays the same in an ideal transformer.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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