Which one of the following statements is correct with regard to the material of electrical insulators ?
- A.They contain no electrons
- B.Electrons do not flow easily through them
- C.They are crystals
- D.They have more number of electrons than the protons on their surface
Correct answer
Explanation
The correct answer is B, Electrons do not flow easily through them. In an insulator the electrons are tightly bound to their atoms, so there are almost no free electrons to carry a current.
Metals such as copper and aluminium have many free electrons that move easily, so they are good conductors. In insulators such as rubber, glass, dry wood, plastic, mica and porcelain, the outer electrons are held firmly and need a very large energy to break free, so they resist the flow of charge. In band theory, an insulator has a wide forbidden energy gap of several electron volts between its valence and conduction bands. This is why wires are covered with plastic or rubber.
A is wrong: every material is made of atoms, and all atoms contain electrons. C is wrong: many insulators, such as glass and rubber, are not crystals at all. D is wrong: an insulator is normally neutral, with as many electrons as protons.
Exam tip: Conductors have free electrons; insulators have bound electrons and a wide energy gap.
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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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
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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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
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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